home Aquarium How to properly supply CO2 to an aquarium

How to properly supply CO2 to an aquarium

Sparkling water

When using ultra-small volumes, this method is one of the most efficient and fastest. This is due to the fact that the soda itself is already a solution of carbon dioxide in water. For objective reasons, sweet water is not suitable. It contains a lot of unnecessary substances that can get into the water and harm. Therefore, it is better to use brands that do not contain sugars, but also do not contain minerals.

The concentration in a closed bottle tends to 10 thousand milligrams per liter. After opening, the gas is released and the number rapidly decreases to 1500 mg / l, but even this is more than enough. For every 10 liters of water, only 20 ml of soda will need to be added.

Don’t be too hopeful, however. The main disadvantage, as in the case of sugar and yeast mash, will be precisely the lack of knowledge of the exact gas concentration. And this complicates the calculation of the optimal dosage.

In addition, oddly enough, this method is the most expensive of all. The price per gram of carbon dioxide is three times higher than that of the closest competitor. Therefore, it is worth considering soda as a way to urgently raise the concentration of the desired indicator to an acceptable value when others are unavailable for some reason.

The use of drugs

One of the most effective reagents is Tetra CO2 Plus, which dissolves easily in water and is distributed as a highly gaseous solution. One pack, for normal use, should be sufficient for 100 uses in a 20 liter aquarium, which means several years of continuous supply of carbon dioxide.

It is easy to supply CO2 to the aquarium. just pour 2.5 milliliters into the water once a week. The gradual release of gas will nourish plants for a long time and support the process of photosynthesis.

  • No need to build bulky structures to function.
  • Ease of operation.
  • Relatively long period of operation of the tool.
  • Preventing excessive algae growth.

At the same time, the plants are saturated with pure carbon dioxide, which has a positive effect on their development and growth dynamics. They stay healthy and actively synthesize oxygen in the water.

CO2 delivery methods

In order to choose the best option, you should know about all the available ones. Each of them differs both in its complexity and in the price for the use and subsequent operation of the installation. If the task is to make a CO2 generator for an aquarium with your own hands, you should not hope for a strong reduction in the cost of the process. Especially if a more reliable, durable and automated method is used.

So, the supply of carbon dioxide to the aquarium can be done in the following ways:

The latter method, of course, does not claim to be more effective, but despite this, an ordinary bottle of water is a rather serious source of carbon dioxide.

Fermentation can provide CO2 supply. an economical option for aquarists on a small budget.

Compressed gas cylinder

Such devices are called differently, but their essence is always the same. to ensure the smoothest possible introduction of gas into the water column so that it does not immediately appear on the surface. For this, they are usually equipped with special flow limiters that start at the moment of switching on. Several options for names:

  • flipper;
  • diffuser:
  • reactor;
  • generator.

They depend primarily on the manufacturer who is trying to draw attention to their product. The principle of operation is more or less similar everywhere.

Special sensors are attached to the cylinder, which measure various indicators of the composition of the water and, on their basis, measure the release of gas. There are models with automatic determination of the pH level using an electrode brought into the water. If the selected model does not have such modules, you will have to constantly monitor the acidity level yourself.

In addition, if pH monitoring is not carried out, then these cylinders control the flow using a special magnetic valve, which releases a strictly metered amount of CO2 on a timer.

If the system has just been installed, do not immediately open the valve to full. This must be done smoothly in order to prevent damage to the thin membrane that is located in the gearbox.

With the help of special sensors attached to the cylinder, it is convenient to monitor the level of important indicators.

How to make a CO2 generator for an aquarium with your own hands

Fish and other creatures living in aquariums are able to eat not only the food that the owner buys and pours into the water, but also the flora that grows in the aquarium. To prevent such plants from withering, they also need to eat something. Optimal for this is carbon dioxide, which is dissolved in water. But in a confined space, water quickly loses it. Therefore, it makes sense to make a CO2 generator for an aquarium with your own hands.

Some aquarium plants need carbon dioxide, which is dissolved in water.

Acceptable concentration levels

For all processes to occur correctly, you need a certain minimum amount of carbon dioxide molecules in water. Despite the fact that the inhabitants of the aquarium also emit this gas during their vital activity, its amount is absolutely insufficient for the course of photosynthesis.

Therefore, it is worth knowing how large the gas concentration should be, so as not to oversaturate the water with it. This will not lead to anything good, since oxygen starvation can occur in living beings at night.

The indicator depends on the volume of the aquarium, but at the same time obeys the law, in which you can derive its average value. It is equal to 2-10 milligrams per liter. For stagnant bodies of water, the indicators may be normal at 30, but everything is too individual.

First of all, you need to know in what conditions the plants that were planted lived. If the state they are accustomed to is a light or almost absent current, then you can add more carbon dioxide and not be afraid of overspending. If they appear only in waters with a tangible current, then you can reduce the dose and nothing bad will happen from this.

The minimum allowable value is at the level of 3-5 milligrams, therefore, 1 mg, which is normal for home conditions, is unacceptable.

The need to produce carbon dioxide

Systems are often assembled that are capable of delivering carbon dioxide to the aquarium water. They often have many uses that are not limited to this. They are involved in many processes, for example:

  • Oxygen production. In addition to nutrients, plants can supply water with this substance during photosynthesis. Thus, the fish that live in the aquarium will breathe normally and will not die from lack of oxygen.
  • PH control. The acidity rises slightly, thereby reducing its value. This creates much more acceptable conditions for the normal functioning of all living things inside.

It is worth noting that it is impossible to completely shift the work of saturating the water with oxygen to the plants. At night, in the absence of sunlight, which is needed for the formation of glucose from carbon dioxide, the process will not start. Therefore, an aerator is definitely needed. a mechanism that can automatically supply air into the water, after which some amount of oxygen will dissolve in it and prevent the living creatures from perishing inside.

In addition, in the dark, plants absorb it instead of producing O2, causing a reverse reaction in their cells. With it, carbon dioxide and water are released, which means that the need for the delivery of breathing mixture increases even more.

How To Set Up Aquarium Co2 System. The EASY Way

Use of fermentation

Injecting CO2 into an aquarium with this reaction can help aquarists on a budget, as no expensive components or complex reagents are used. All that is needed is to assemble several components:

  • Sugar. about 300 grams.
  • Yeast. less than a gram, it is better to stick to a ratio of 1: 1000 and take the amount based on the weight of sugar. In this case, they should be 0.3 grams.
  • Water. 1 liter, shaking the mixture is not allowed.
  • Plastic bottle, with a volume of one and a half liters.
  • Sufficient tubing.

The design is extremely simple. a hole is made in the bottle cap, a tube is inserted into it, the other end of which is lowered into the water. Through it, the gas released as a result of the reaction will enter the aquarium and saturate it.

If at the same time the bottle with the mixture will hang vertically above the aquarium, then it is better to attach an additional tank to the system. Over time, mash is formed in the main tank, which can be picked up by carbon dioxide and sent into the water. This is unacceptable, as the dissolution of sugar will only harm the inhabitants. It is better to attach another container to the system, into which gas and possible lumps will first enter.

However, it is impossible to say with absolute certainty how much carbon dioxide enters the aquarium: the reaction simply proceeds without the slightest control and can be very uneven due to the fact that the mixture itself emits gas inhomogeneously. In addition, the capacity will have to be changed every two weeks, since it is after this time that the reaction completely stops.

The use of special preparations can be an effective substitute for the fermentation technique.

CO2 in the aquarium. The role of carbon dioxide and how it is fed into the aquarium.

Why do you need CO2 in an aquarium? Everyone knows from the school biology course that the main source of plant nutrition is carbon dioxide CO2. In natural reservoirs, plants use CO2 dissolved in water. over, due to the huge volume of water, the concentration of CO2 in natural reservoirs is quite constant, which cannot be said about home aquariums. If plants grow in the aquarium, they very quickly consume all the dissolved CO2 from the water and the restoration of the previous CO2 concentration in the aquarium water does not occur by itself, since the aquarium is a closed system. Aquarium fish exhale only a tiny fraction of CO2. As a result, the growth of aquarium plants stops. In addition, water with low m CO2 has a high pH, ​​which further damages the aquarium plants. I think many aspiring hobbyists have noticed that tap water has a lower pH than it does when added to a plant aquarium. This is because CO2 forms carbonic acid in the water, which lowers the pH. This means that the more CO2 in the water, the lower the pH.

In order to maintain a constant concentration of CO2, as in natural reservoirs, it is necessary to supply carbon dioxide artificially. There are several types of CO2 supply systems for an aquarium. Each of these system methods has its own advantages and disadvantages. All of them will be listed below and you can choose the most suitable method for your aquarium.

Soda as a CO2 source for your aquarium

For nanoaquariums up to 20 liters, not everyone wants to communicate with a CO2 balloon installation. You can make a CO2 generator using mash or soda. But you can do it easier. There is an ancient and undeservedly forgotten method of CO2 supply. the use of carbonated water. Carbonated water is a kind of concentrate of carbon dioxide already dissolved in water. CO2 in soda is usually about 5000-10000mg / l, and after opening the bottle it tends to 1450mg / l. If you calculate how much carbonated water is needed to bring the CO2 concentration in the aquarium to 10 mg / l, then it comes out quite economically. Fresh soda only needs 20ml per 10L of aquarium water, which will give 10mg / L of CO2 in the aquarium. It is enough just to apply soda in the morning along with fertilizers. After standing, soda can be added in large quantities, since carbon dioxide is eroded. Approximately 1 liter of soda is enough for 10-20 liters of aquarium for a month. Any sparkling water will do, except for salt water, of course. It is better to use the cheapest ones. They are usually made from tap water :). It is better not to increase the CO2 concentration by this method to more than 10 mg / l. First, it is not known how much carbon dioxide your soda contains, 5000mg / L or 10000mg / L. Secondly, large fluctuations in CO2 concentration in the aquarium are not desirable. After adding soda, the concentration will gradually decrease due to the consumption of the aquarium plants. Constant fluctuations of CO2 from 10 mg / l to zero and back are not terrible. But fluctuations from 20-30mg / l to zero are much worse for balance in the aquarium.

  • no need for a reactor to dissolve CO2 and a bubble counter, since CO2 is already dissolved in carbonated water;
  • ease of use;
  • economical in the short term;
  • suitable for nano aquariums.
  • unstable concentration of CO2 in the aquarium;
  • the price of 1 gram of CO2 is the highest of the listed methods, that is, uneconomical in the long term and for large aquariums;
  • poor CO2 supply in comparison with other methods.
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CO2 cylinder installation for aquarium.

For large aquariums, the most optimal method of supplying CO2. this is carbon dioxide from a balloon installation. The CO2 cylinder supply system consists of a cylinder and a control system, which includes: a reducer (1), a solenoid valve (2), a fitting (3), a coil with a connector (4) providing the operation of the solenoid valve, a pneumatic throttle (5) for fine adjustment of the tempo CO2 supply, power supply unit (6). Such an installation can be assembled by hand. But there are also ready-to-use installations on sale, however, they are several times more expensive.

properly, supply, aquarium
  • cost-effectiveness in the long term;
  • large supply of CO2;
  • full control of the intensity of CO2 supply;
  • stable CO2 supply;
  • possibility of automation (by connecting a pH controller).
  • the complexity of the assembly;
  • high cost of equipment;
  • the need to work with a high pressure cylinder.

CO2 for a mash aquarium

Such a generator mainly consists of a hermetically sealed vessel with a wash and a tube for CO2 outlet. A plastic bottle can act as a vessel. Sometimes they use an additional trap from a second plastic bottle, in case the wash foams and comes out of the bottle. The trap prevents mash from entering the aquarium.
The mash itself can consist of 300 grams of sugar (not dissolved), 0.3 grams of SafLevur dry yeast (for drinks and pastries), 1 liter of water in a 2 liter bottle. Sometimes sugar is dissolved together with gelatin in 0.5 liters of water and 0.5 liters of a mixture of yeast and warm water is poured on top of it. As a rule, such mash plays no more than two weeks. Variations of mash recipes are just a sea, but rarely when it is possible to add her work for more than 2-3 weeks.

  • ease of assembly;
  • low cost of materials for assembly;
  • security.
  • instability of CO2 supply;
  • low resource;
  • no feed control.

CO2 generators

Another type of CO2 supply is the use of a CO2 generator. There are two types of CO2 generators. The first is home brew. The second is a chemical generator using the reaction of carbonates with an acid. Both methods are suitable for medium-sized aquariums up to 100 liters. In large aquariums, and even more so with a high planting density of aquarium plants, the intensity of CO2 generation may not be enough.

CO2 generator from citric acid and soda.

Unlike home brew, such a CO2 generator provides a more stable supply of carbon dioxide. Because it is much easier to implement a uniform addition of a citric acid solution to a soda solution with the release of CO2 than a uniform sugar fermentation process.

There are different designs of such CO2 generators. The most interesting option is executed according to the following scheme, taken from the manufacturer’s website 51co2.com (In runet, it can be found as Yuri TPV CO2 Generator):

The essence of such an installation of a CO2 generator is that citric acid flows from vessel A to vessel B with soda, and CO2 is formed. The resulting carbon dioxide creates an increased pressure in both vessels, since they are connected by a 2-1-10-9 channel with check valves at both ends (3 and 8). over, valves 3, 8 and 7 ensure the movement of CO2 in only one direction. from vessel B to A and into the aquarium, but not vice versa. As soon as CO2 leaves the generator, the pressure decreases in channel 2-1-10-9 and vessel B, but not in vessel A (valve 3 delays it). Therefore, the increased pressure in vessel A squeezes citric acid from vessel A into vessel B and CO2 is generated again.
The generation intensity is regulated by the needle valve D.

  • low cost of materials for assembly;
  • security;
  • satisfactory stability of CO2 supply;
  • the ability to control the intensity of CO2 supply.

Do you need to use co2 in your Planted Aquarium?

  • the complexity of assembly, despite the cheapness of materials;
  • low resource;
  • low intensity of CO2 supply.

For the listed CO2 supply systems, a reactor is required, with the help of which CO2 is dissolved / sprayed in the aquarium, and a bubble counter, with which the amount of CO2 supplied to the aquarium is controlled. There are a huge variety of reactors operating on different principles. The simplest and most effective option is to supply CO2 to the inlet of the internal filter in the aquarium. Interesting options are discussed in the forum thread Choosing an Effective Reactor. But not all methods of CO2 supply require the use of reactors. Read about it below.

What should be the concentration of CO2 in aquarium water?
How much CO2 should be fed to the aquarium?

In natural reservoirs, the concentration of CO2 ranges from 2 to 10 mg / l (in running waters) and can reach 30 mg / l in stagnant waters of bogs. Tap water usually contains 2-3 mg / l of CO2. In an aquarium with plants and without CO2 supply, its concentration is usually less than 1 mg / l or tends to zero altogether.

It should be quite obvious that aquarium plants need the same conditions that they have in their natural habitat. For some species it is 2-10 mg / l, and for some it is better 20-30 mg / l. That is, at least in the aquarium, it is necessary to increase and maintain the CO2 concentration at the level of 3-5 mg / l. The maximum is 30 mg / l, as aquarium fish and shrimp can be harmed at higher concentrations. CO2 concentration can be assessed using a long CO2 test. dropchecker.

The growth rate of the aquarium plants can also be controlled by varying the CO2 concentration in the aquarium water. But it is better to do this in conjunction with changing the lighting level. If instead of CO2 concentration in the range of 20-30 mg / l, you decide to make 10-15 mg / l, then it is better to reduce the lighting level from 1 watt / l to 0.5 watt / l.

The bubble counter is a must, as it can be used to estimate the amount of CO2 supplied to the aquarium. It is better to count bubbles within a minute to determine the rate in the most commonly used dimension of bubbles per second (p / s).

And the last, also important question regarding CO2 in an aquarium is taken out in a separate article: determining the concentration of CO2 in an aquarium.

You can discuss the article or ask the author a question on the forum

CO2 for the aquarium. Carbon dioxide and pH of water.

How to correctly and how much to supply carbon dioxide (CO2) to the aquarium.

Carbon dioxide. CO2 and pH. pH of the water in the aquarium, or how to prevent stalagmites from growing on the leaves of aquarium plants.

Carbon dioxide, or carbon dioxide (CO2), is vital for plants. Plant carbon is obtained precisely from CO2, during the process of photosynthesis, and carbon atoms are the main building blocks for organic molecules. And aquarium plants are no exception. With a shortage of carbon dioxide, they will simply have nothing to build their tissues from, which will greatly slow down or completely stop their growth. On the other hand, with an excess of carbon dioxide in the aquarium water, the fish begin to suffocate even when there is a lot of oxygen in it. This is due to two very unpleasant effects: Bora and Ruta, which are caused by a change in the properties of fish hemoglobin with a high content of carbon dioxide. Consequently, the aquarist, if only he wants to admire living, and not plastic plants and fish, must be able to maintain the concentration of CO2 in the water of his aquarium in the optimal range. so that plants can grow well and fish can breathe normally. How to do this will be described in this article.

For those who do not want to delve into the essence of the matter, but want to immediately get an answer: the optimal carbon dioxide in the aquarium water is 15.20 mg / l. How much CO2 is dissolved in your aquarium water can be calculated from the pH and carbonate hardness of the water. KN. In order not to count anything yourself, but only to substitute the pH and KH values ​​determined with the help of tests into the necessary windows and get an answer, use a special counting rink.
Does the aquarist really need to measure something and then calculate something? Is it really necessary to “check harmony with algebra”? After all, everything in nature is capable of self-regulation. The aquarium is also essentially a small “piece” of nature and natural harmony can be established in it by itself. In an aquarium of normal (classical) proportions with sufficient but not excessive numbers of fish, biological equilibrium occurs naturally. In order for it to remain stable, it is necessary not to overfeed the fish; change about a fifth of the water volume regularly and at least once a week. And it will really provide a stable biobalance. In such an aquarium, fish in the course of their vital activity will emit as much carbon dioxide, ammonia and other substances as is necessary so that the plants receive the necessary mineral nutrition and do not live in poverty. In turn, healthy plants will provide the fish with adequate oxygen. Since the last quarter of the IXX century (since the time of N.F. Zolotnitsky) and throughout most of the XX century, almost all aquarists had such aquariums and everything was fine with them. And what tests for measuring the most important parameters of aquarium water are, many of them did not know at all. Modern aquarium keeping is simply unthinkable without the use of means for determining the parameters of aquarium water (without tests).
What has changed? Technical capabilities! With the help of special equipment, we began to deceive nature. In a small glass box, which in fact is a typical indoor aquarium (and even a solid volume of 200-300 liters for an indoor reservoir compared to a natural reservoir is very small), it became possible to contain such a number of living organisms that is in no way commensurate with the natural resources in it. available. Take oxygen: how is it naturally replenished in water? We have already mentioned photosynthesis, but this is during the day, and at night? Without mixing or aerating the water with the help of technical devices, the replenishment of oxygen reserves in the water is very slow. So in the completely still water of the aquarium at its very surface. at a depth of 0.5-1 mm. the amount of oxygen can be double that at a depth of just a few centimeters. The transition of oxygen from air to water itself occurs extremely slowly. According to the calculations of some researchers, an oxygen molecule, due to diffusion alone, can deepen by no more than 2 cm per day! Therefore, without pumps and aerators, which in ancient times did not exist, it was simply impossible for the aquarist to populate the aquarium with “extra” fish. they would suffocate. Modern equipment allows you to keep an unthinkable number of fish in former times, and bright lamps very tightly plant the aquarium and even cover its entire bottom with ground cover plants!

This is a fragment of the bottom of a modern aquarium. It is densely planted with ground cover plants: Glossostigma elatinoides, Javanese moss (Vesicularia dubyana) and Riccia fluitans. The latter usually floats near the surface, but it can be achieved (and this is implemented here) so that it grows at the bottom. To do this, the aquarium needs to be brightly lit and supplied with carbon dioxide. CO2. Amano’s shrimp also did not accidentally get into the frame, who needs to carefully and carefully select the remnants of food from the thick of the flyers.

But we must not forget that the deceived nature from the very moment when we super-densely populated the aquarium with living organisms is no longer responsible for anything! The sustainable viability of such a system is now far from guaranteed. For the ecological chaos that the aquarist has arranged in his aquarium, he and only he will be responsible. Even a minor mistake will lead to an environmental disaster. And in order not to be mistaken, you need to know what plants and fish need and what hydrochemical parameters of water suit them. Timely control of oxidation. pH, KN, in ammonia water. nitrite. nitrates and phosphates, potassium and iron ions, you can quickly interfere with the work of an overpopulated and therefore unstable system, supplying it with missing resources and removing excess waste that the aquarium “biocenosis” itself is not able to utilize. Carbon dioxide is one of the most important and necessary resources for an aquarium with living plants. CO2.

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Photo taken at a workshop held by Takashi Amano in 2003. This is a rear view of the aquarium. An artificial background is not provided here. It will be created by plants that are extremely densely planted along the back wall. In order for them to grow without “strangling” each other, several tricks based on aquarium high technologies were used at once. This is a special multi-layer non-acidifying soil rich in minerals available to plants, a very bright light source with a specially selected spectrum, and of course a device that enriches the water with CO2: a cylinder with a reducer, a bubble counter, a carbon dioxide atomizer (reactor). all manufactured by ADA.
Part of the system that enriches the aquarium water with CO2. close-up. A device is attached to the outside that allows you to visually monitor the gas supply to the aquarium. bubble counter. There is a diffuser inside. For clarity, the organizers of the seminar turned on the gas very strongly and a whole column of bubbles rose from the diffuser. Aquarium plants don’t need that much carbon dioxide. In normal operation, much less gas is supplied. Thus, the lush vegetation in Takashi Amano’s “natural” aquarium does not grow by itself. this requires special equipment. So this aquarium is not so “natural”, it is rather technogenic!
properly, supply, aquarium

There is very little CO2 in the earth’s atmosphere. only 0.038%. In dry atmospheric air at standard barometric pressure (760 mm Hg), its partial pressure is only 0.23 mm. rt. Art. (0.038% of 760). But even this very small amount is quite enough for carbon dioxide to indicate its presence in an important way for the aquarist. For example, distilled or well-demineralized water, after standing in an open container for a sufficient time to dissolve in it and come into equilibrium with atmospheric air, the gases of which this air consists, will become slightly acidic. This will happen because carbon dioxide will dissolve in it.
At the above-mentioned partial pressure of carbon dioxide, its concentration in water can reach 0.6 mg per liter, which will lead to a decrease in pH to values ​​close to 5.6. Why? The fact is that some carbon dioxide molecules (no more than 0.6%, but this is enough to drop the pH) interact with water molecules to form carbonic acid:

Carbonic acid dissociates into a hydrogen ion and a bicarbonate ion:

That is why the acidification of distilled water occurs. Recall that the pH (active reaction of water) reflects the hydrogen ions in water. This is the negative logarithm of their concentration.
In nature, raindrops are acidified in the same way. Therefore, even in ecologically clean regions where there is no sulfuric and nitric acids in rainwater, it is still slightly acidic. Then passing through the soil, where carbon dioxide is many times higher than in the atmosphere, the water is even more saturated with it. Then interacting with rocks containing limestone, such water converts poorly soluble calcium carbonate into readily soluble bicarbonate:

This reaction is reversible. It can be shifted to the right or to the left, depending on the concentration of carbon dioxide. If CO2 remains stable for a sufficiently long time, then a carbon dioxide-lime equilibrium is established in such water: new hydrocarbonate ions are not formed.
Carbon dioxide-lime equilibrium can be formed at different pH values, and the ratio of the concentrations of the CO3 2- ions present in the water. HCO 3. and free carbon dioxide (CO2) will depend on the pH of the aqueous solution (in our case, the pH of the water in the aquarium) and temperature. This dependence on the pH at 25 ° C is shown in Fig. one.

Fig 1. Ratio of CO3 2-. CO2 and HCO 3. at a temperature of 25 ° C. It can be seen that carbon dioxide as such (free carbon dioxide, or CO2) can be present in water only if pH a at pH values ​​less than 4.3 is all dissolved in water carbon dioxide is represented only by free carbon dioxide. At pH8.4, there is no free carbon dioxide in the water. The bicarbonate ion (semi-bound carbon dioxide) is present in water with a pH value greater than 4.3, at pH = 8.4 all carbon dioxide is in a semi-bound form (HCO 3.). At pH8.4, CO3 2- ions (bound carbon dioxide) appear in water. the concentration of which increases with increasing pH.
Based on materials from the website of the Department of Water and Fuel Technology of NRU MEI.

If carbon dioxide is added to the equilibrium system, then the calcium-lime equilibrium will be disturbed, which will lead to the dissolution of calcium and magnesium carbonates. When applied to aquarium conditions, this means that snail shells, as well as limestone soil, rocks and decorations, will begin to dissolve. in such cases aquarists say. “phonite” soil. Running a little ahead, I will note that “fluorescent” soils and decor are unsuitable for aquariums with an additional supply of CO2 to the water. And why so, will be explained below.

If CO2 is removed from the equilibrium system in one way or another, then calcium carbonate will precipitate from the solution containing bicarbonates. This happens, for example, when boiling water (this is a well-known way to reduce carbonate hardness, that is, the concentration of Ca (HCO3) 2 and Mg (HCO3) 2 in water. The same process is observed with simple settling of artesian water, which was underground with increased pressure and a lot of CO2 has dissolved in it.Like soda in an open bottle, once on the surface, this water gives off excess carbon dioxide until its concentration matches the partial pressure of CO2 in the surrounding air. Stalactites and stalagmites are formed according to the same principle: water oozing from underground layers is freed from excess carbon dioxide and at the same time from calcium and magnesium carbonates, which precipitate, increasing the stalactite in size. the reaction occurs on the leaves of many aquarium plants, when they actively photosynthesize in bright light, absorb all the carbon the liquid gas dissolved in the aquarium water. This is where their leaves begin to “turn gray”, as they become covered with calcium carbonate sediment (see how it looks in another article). But since all the carbon dioxide has been extracted from the water, then there is no more carbonic acid in it. If there are no other acids in the water in a significant amount, then the pH should rise. Which is what happens. Actively photosynthetic plants, having consumed all the CO2 available in the water, can raise the pH of the aquarium water to 8.4. With such an indicator of the active reaction of water, there are no longer free molecules of carbon dioxide and carbonic acid in it, therefore, in order to continue photosynthesizing, plants are forced to extract carbon dioxide from bicarbonates. However, not all types of aquarium plants can do this, although many can.

As a rule, they cannot noticeably raise the pH even higher, since further growth of this indicator greatly impairs the functional state of the plants themselves: photosynthesis, and therefore the removal of CO2 from the aquarium water, slows down, and the carbon dioxide in the air, dissolving in the water, stabilizes the pH. Aquarium plants, therefore, can literally choke each other. The winners are those species that better extract carbon dioxide from hydrocarbons, and those who do not know how to do this, for example, rotals, pogostemons and aponogetons, suffer. It is these plants that are considered the most delicate among aquarists.

Those plants that can extract CO2 from hydrocarbons are more tenacious. These include rdest, vallisneria, echinodorus, nayas, hornwort. However, dense thickets of elodea are capable of strangling them. And all because Elodea can extract carbon dioxide bound in bicarbonates even more efficiently:

This process can lead to an increase in the pH value of aquarium water to 10, which is dangerous not only for other plants, but also for the vast majority of aquarium fish.
It is impossible to grow a number of plants in aquarium water with high pH values, and many species of aquarium fish definitely do not like alkaline water: in it they can get sick with flexibacillosis and branchiomycosis. There is even a special non-contagious fish disease that is caused by alkaline water. alkalosis. Especially destructive are the sharp daily fluctuations in the pH value that occur in bright light and are caused by the activity of plants that extract carbon dioxide from bicarbonates.
Is it possible to correct the situation by increasing the aeration of the aquarium, in the expectation that due to the high solubility of carbon dioxide, the water in the aquarium will be enriched with CO2? Indeed, at normal atmospheric pressure and a temperature of 20 ° C, 1.7 g of carbon dioxide could dissolve in one liter of water. But this would happen only if the gas phase with which this water was in contact were entirely composed of CO2, that is, the partial pressure of carbon dioxide would be all 760 mm of mercury. And upon contact with atmospheric air, which contains only 0.038% CO2, only 0.6 mg can pass from this air in 1 liter of water. this is the equilibrium concentration corresponding to the partial pressure of carbon dioxide in the atmosphere at sea level. If the concentration of CO2 in the aquarium water is lower, then aeration will indeed raise it to 0.6 mg / l, but no more! However, usually carbon dioxide in the aquarium water is still higher than this value and aeration will only lead to a loss of CO2.
The problem of carbon dioxide deficiency can be solved by supplying it to the aquarium, especially since it is by no means difficult. In this case, you can do without even expensive branded equipment, but simply use the processes of alcoholic fermentation in a sugar solution with yeast and some other extremely simple devices.
Here, however, one must be aware that by this we are deceiving nature once again. Thoughtlessly saturating the aquarium water with carbon dioxide will not lead to anything good. So you can quickly kill fish, and then plants. The process of supplying carbon dioxide must be strictly controlled. It was found that for fish the concentration of CO2 in the aquarium water should not exceed 30 mg / l. And in a number of cases, this value should be reduced by at least another third. Recall that fluctuations in the pH value for fish and plants are harmful, and a strong supply of carbon dioxide quickly acidifies the water.
How to estimate CO2 and ensure that when this gas is supplied to the aquarium, the pH values ​​fluctuate slightly and remain within the acceptable range for both fish and plants? Here we cannot do without formulas and mathematical calculations: the hydrochemistry of aquarium water, alas, the topic is rather “dry”.
The relationship between the concentrations in freshwater aquarium water of carbon dioxide, hydrogen ions and bicarbonate ions in the pH range from 5 to 8.4 reflects the Henderson-Hasselbach equation. which in relation to our case will look like:

where K1 is the apparent dissociation constant of carbonic acid in the first stage, taking into account the equilibrium of ions with the entire amount of carbon dioxide in water. the total analytically determined carbon dioxide (that is, both simply dissolved CO2 molecules and hydrated molecules in the form of carbonic acid. H2CO3). For a temperature of 25 ° C, this constant is 4.4510.7. Square brackets represent molar concentrations.
Converting the formula gives:


The pH and [HCO3. ] can be determined using standard aquarium pH and KH tests. [HCO 3.] in aquarium water determines the carbonate hardness test: KH test. It should be noted that the word “stiffness” is in its name. just a tribute to tradition. It has no direct relation to the determination of the concentrations of calcium and magnesium ions. In fact, the KH test determines the alkalinity of water (more on this in a separate article). In an ordinary aquarium, if buffer solutions such as KH and pH and gummates were not added to the water, it is bicarbonate ions that make the main contribution to alkalinity, so the KH test is quite suitable for our purposes. The only inconvenience of its use is associated with the need to recalculate the degrees in which it gives the result, in molar concentrations (M), which, however, is not at all difficult. For this, the value of carbonate hardness in degrees is sufficient. received after the testing procedure, divided by 2.804. The concentration of hydrogen ions, expressed in the value of the pH indicator, must also be converted to M, for this it is necessary to raise 10 to a power equal to the pH value with a negative sign:

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To convert the [H2CO3 CO2] value calculated by formula (2) from M to mg / l CO2, multiply it by 44000.
We must not forget that using the Henderson-Hasselbach equation, it is possible to calculate the concentration of the total analytically determined carbon dioxide in the aquarium if the aquarist did not use special reagents and humic and other organic acids in his aquarium to stabilize the pH. This can be judged by the color of the aquarium water: if it does not look like the “black waters” of the Amazon, that is, it is colorless or only slightly colored. It means that there are not many of them there).
Those who are on a short foot with a computer, in particular with Excel spreadsheets, can, on the basis of the above formula and the K1 value, compile detailed tables reflecting carbon dioxide depending on carbonate hardness and pH. We will give here an abbreviated version of such a table and a calculator that will automatically calculate carbon dioxide in water, but we hope it is useful for hobbyists:

The minimum pH values ​​of the water in the aquarium for a given carbonate hardness, at which carbon dioxide is not yet dangerous for fish (red numbers in the columns), and the maximum allowable pH values ​​at which plants that cannot extract CO2 from hydrocarbons, although slowly, still grow (green numbers in columns). For 25 ° C.

Carb. tough. KH 0.5 one 2 3 four five 6-7 8-9 10-11 12-13
Mol / l 0.18 0.36 0.71 1.07 1.43 1.78 2.14-2.5 2.85-3.21 3.57-3.92 4.28-5.35
min pH for fish
(25-28 mg / l CO2)
5.8 6.1 6.4 6.6 6,7 6.8 6.9 7.0 7.1 7.2
max pH for plants
(6-7 mg / l CO2)
6.4 6,7 7.0 7.2 7.3 7.4 7.5 7.6 7,7 7.8
“Natural” pH
(2-3 mg / l CO2)
6.8 7.1 7.4 7.6 7,7 7.8 7.9 8.0 8.1 8.2
pH corresponding to the partial pressure of carbon dioxide in the atmosphere
(0.6 mg / l CO2)
7.4 7,7 8.0 8.2 8.3 8.4 _ _ _ _

If you decide to supply carbon dioxide, then use this table to determine the optimal pH value. Select the column corresponding to the carbonate hardness of the water in your aquarium. Adjust the CO2 intake so that the pH value falls between the red and green numbers. For example, if the KH in the aquarium is 4, then the range of acceptable pH values ​​will be 6.7. 7.3. At pH = 6.7, the concentration of carbon dioxide in water will be about 28 mg / l. this is almost the limit for fish and very comfortable for plants. If the concentration of CO 2 is increased a little (the pH value will then become less than the “red” number), then the fish may die. At pH = 7.3, fish, even the most delicate ones, are not threatened with carbon dioxide poisoning, since it will be absolutely safe for them: only about 7 mg / l. This concentration is sufficient for the survival of plants, but they will not demonstrate rapid growth. But with pH values ​​from the middle of the range of permissible values, for example, at 6.9 (the concentration of CO2 will be about 17 mg / l), both fish and plants will feel great. To maintain such values ​​is exactly what you need to strive for. For this, the supply of CO2 is reduced if the pH value tends to the lower limit and is increased if it approaches the upper one. During daylight hours, the active response of water usually gradually changes, since the amount of carbon dioxide supplied rarely matches the needs of plants: the concentration of gas either slowly rises or falls. The initial setting to the middle of the interval will help to ensure that the pH value does not jump out of its borders. If the supply of CO 2 is regulated by a pH controller that automatically shuts off the supply of carbon dioxide when the pH drops to a predetermined level, then this level should be set so that it is not lower than the permissible for fish (red numbers in the table). The use of a pH controller is most efficient and safe, but it is relatively expensive and the supplied pH electrode needs monthly calibration.

In the foreground of this photograph is another Rotala wallichii. Left. river lighthouse (Mayaca fluviatilis). She is also a lover of free carbon dioxide in water. With suitable lighting and a carbon dioxide content in the aquarium of the order of 15-20 mg / l, these aquatic plants are covered with oxygen bubbles, so photosynthesis is so efficient. The water turns out to be oversaturated with oxygen. It should be especially noted that this abundance of oxygen will not protect fish from death in the event of an overdose of CO2.

You can organize the supply of CO2 into the aquarium not only with a CO2 bottle, but also with the help of special tablets placed in the aquarium in a special device (sera production), with the help of a scrubber, with an electronic device that generates carbon dioxide from a carbon cartridge and another simple device. In the simplest version, in order to saturate the water with carbon dioxide, you can pour slightly mineralized carbonated water into the aquarium at the beginning of daylight hours (of course, without food additives!). In small aquariums this can have a visible positive effect.

If you do everything right, it can turn out very well, isn’t it? Without the supply of carbon dioxide to the aquarium, such a design would be simply impossible. Densely planted with rapidly growing aquatic plants “herbalist” requires a mandatory daily supply of CO2.
Designed by Evgeny Borovik. about Borovik’s style.

The table also shows the pH values ​​that, at a given carbonate hardness, a well aerated water in a room aquarium acquires (“natural” pH level), if it is moderately populated by fish and if the water oxidizability in it is not high. In other words, if the supply of carbon dioxide to the aquarium is suddenly stopped, and the aeration is turned on “to full”, then it can be expected that the pH of the water within a few hours will increase approximately to these values. As can be seen from the table, the difference from the lower limit of the permissible interval to the “natural” pH level is approximately equal to 1. For delicate species of shrimp, fish and plants, it may be too strong and, if it does not cause their death, it will have a depressing effect. An automatic pH controller does not allow such differences, but if there is no controller, then they are quite likely. Therefore, if at night you stop supplying CO2 to the aquarium and turn on aeration, then be careful: the pH can rise too sharply. To prevent this, do not adjust the carbon dioxide supply so that the pH value is close to the lower (“red”) border of the permissible interval, because it is quite enough to keep to its middle and then the difference between day and night pH values ​​will not exceed 0.5, which is absolutely safely. Strong aeration at night is also not always necessary. But only observations of the aquarium will make it possible to establish whether it is necessary (in many cases, the water flow from the filter pump is quite enough to ensure sufficient gas exchange).
The numbers in the last line of this table are the pH of water of a given carbonate hardness, in equilibrium with the partial pressure of CO2 in the atmosphere. It can be seen that they are even higher. In natural reservoirs, in the rapids of clean rivers, where water boils and releases all excess (non-equilibrium) carbon dioxide into the atmosphere, such pH values ​​do indeed take place. In the premises, the partial pressure of carbon dioxide in the air is higher than in the open air, and the processes taking place in the soil and filter of the aquarium lead to the formation of carbon dioxide. This provides more than in natural conditions, CO2 in the water of aquariums and the water in them with the same carbonate hardness turns out to be more acidic.
Now let’s look at another important question: at what initial pH values ​​of the water in the aquarium can carbon dioxide be supplied to it? To do this, again refer to Figure 1 and our useful plate. Let us recall that the hydrochloric acid, which is formed by dissolving atmospheric carbon dioxide in water, lowers the pH of distilled water, whose KH is close to 0, to 5.6, and water with a carbonate hardness, for example, equal to 5 kN, being in equilibrium with atmospheric gases. has an active reaction 8.4. The following pattern can be easily traced: the higher the carbonate hardness of water, the more alkaline it is. As can be seen from the figure, at pH values ​​greater than 8.4, carbonate ions (CO3 2-) are present in the water, which reacting with free carbon dioxide, will convert its semi-bound form (HCO 3.), which is inaccessible to delicate species of aquarium plants. We’re wasting carbon dioxide. For the same reason, “fluorescent” soils are not suitable for herbal aquariums. By feeding carbon dioxide into an aquarium with such a soil, we will again spend it on the formation of bicarbonate ions. HCO 3. In addition, high pH values ​​in principle inhibit the vital functions of many species of aquarium plants, but they are excellent at promoting the growth of algae. If you have tap water in your home with a high pH value and therefore a high carbonate hardness, then it is not suitable for a herbal aquarium with an additional supply of carbon dioxide. You will have to use a reverse osmosis installation to reduce its mineralization and how to do this is described separately.

So, water with a high pH value is not suitable. And low? Also not suitable, since the carbonate hardness is also too low. Let’s explain why this is bad. It can be seen from the figure that at pH = 6.4 the concentrations of free carbon dioxide and bicarbonate ion are approximately equal, and at a low “carbonate” they are quite small. this is clearly seen from the plate: KN = 0.5. pH = 6.4. and CO2 is only 6 mg / l. it is only enough for surviving delicate plants. Saturation of water with carbon dioxide to a comfortable concentration of 28 mg / l will lead to a drop in pH to 5.8. For many fish, this is the pH value. dangerous limit. it is no longer possible to fall below, otherwise, due to the Verigo-Bohr effect, the fish will begin to experience a lack of oxygen and die. However, the whole point is that with a low carbonate hardness, it is extremely easy to fall below this limit: a slight overdose of CO2 and that’s it.!
Thus, theory tells us that the range of carbonate hardness values ​​most suitable for a herbal aquarium with an additional supply of carbon dioxide lies in the range of 2-4 about KN. This is also confirmed by the practical experience of aquarists. Theory and practice are unanimous on this issue. Indeed, at optimal CO2 concentrations for fish and plants (this is 15.20 mg / l), the pH values ​​will be within 6.6. 6.7. if you care more about plants than about fish, then you can lower the pH to 6.4. This pH value will not cause poisoning (acidosis) in fish suitable for a CO2 herbalist, uncomfortable for algae and good for many aquarium plants.

What equipment is needed to supply carbon dioxide to an aquarium? Here it is best to refer to the practical experience of our members of the forum. Read: CO2 for the aquarium.

The classical proportions of the aquarium are as follows: the width is equal to or not more than a quarter less than the height. The height does not exceed 50 cm. The length, in principle, is not limited. An example is an aquarium 1 m long, 40 cm wide and 50 cm high. The biological balance in such a room reservoir is relatively easy to establish. You can read about specific models of aquariums with the correct proportions here.
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By equilibrium with atmospheric air, we mean such a state of water when the concentrations (stresses) of gases dissolved in it correspond to the partial pressures of these gases in the atmosphere. If the pressure of any gas decreases, then the molecules of this gas will begin to leave the water until the equilibrium concentration is reached again. Conversely, if the partial pressure of a gas above water increases, then more of this gas will dissolve in water.
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