CO2 - how to provide the plants in the aquarium with proper nutrition

Just as oxygen is important for people and fish, hydrogen dioxide (CO₂) is important for aquarium plants. It is no secret that the main building material for plants is sugar - it is obtained from light, water and, most importantly, carbon dioxide. Oxygen, which is so important for living things to breathe, is a byproduct of photosynthesis Life on the planet is built on the basis of this process.

CO₂ for aquarium

Important ! Aquarium plants require carbon dioxide dissolved in water. Its constant supply is provided by a layer of silt covering the bottom of rivers, ponds and lakes. But if we talk about aquariums , here it is produced during bacterial decomposition. Depending on them, plants can grow healthy and strong. Therefore, CO₂ is very important for an aquarium, because the health of the fish depends on the condition of the plants. More information about adding carbon dioxide to the aquarium will be discussed in this article.

Carbon dioxide is the most important condition for the development of aquatic plants

Life on Earth is carbon-based - the main component of most organic substances is carbon compounds.
If animals consume everything necessary for the construction of body tissues with food, then most plants synthesize the “building material” on their own. The process by which plants produce the simplest carbohydrate (glucose) is called photosynthesis. His main reaction:

6CO2 + 6H2O = C6H12O6 + 6O2

Synthesis occurs with the absorption of energy; the formation of each glucose molecule requires about 674 cal. Plants obtain it through absorption by molecules of chlorophyll and other pigments (chromophylls).

Subsequently, the simplest carbohydrates under the action of enzymes are converted into;

• more complex sugars;
• amino acids, proteins, fats, the synthesis of which requires macro- (nitrogen, phosphorus, potassium) and microelements.

This ensures plant growth, development of the root system, accumulation of leaf mass, etc.

Some plants can use other compounds as a carbon source. For example, some aquatic plants (elodea, vallisneria, hornworts, anubias, echinodorus and some others) have adapted to the consumption of bicarbonate ions (HCO3-) and carbonates (CO32-), the presence of which is due to a non-zero concentration of hardness salts.

Thus, several factors are necessary for the development of a plant:

• Availability of water (irrelevant for aquatic plants, since water is their native habitat).
• The source of carbon, for most, is CO2.

• Energy (read lighting).
• Macro- and microelements.

Aquarium plants practically do not experience problems with light energy and nutrients. For most of them, natural daylight and substances stored in the soil are sufficient. For the more demanding ones, it is easy to organize artificial lighting and fertilization. There are certain problems with the main building element (carbon).

Cause of lack of carbon (carbon dioxide)

The deficiency of carbon compounds in artificial domestic reservoirs is explained quite simply.

Under natural conditions, the sources of carbon in water bodies are:

• Carbon dioxide from the atmosphere . CO2 dissolves in water much better than oxygen, but is also easily released. Moreover, due to the large contact area of ​​the water surface with air, the concentration of CO2 obtained from this source can be quite high.

• Salts (carbonates) of various elements . Along with sparingly soluble sources, easily soluble ones (for example, sodium salts) are also brought into water bodies.
• Carbon dioxide released during breathing by representatives of aquatic fauna . This source also provides an intensive supply of CO2.

As a result, the concentration of carbon dioxide in natural reservoirs can range from 3 to 10 mg/l (in flowing water) and up to 30 mg/l in stagnant water bodies. This is quite enough for the growth of aquatic plants.

In home aquariums, even of significant size, the picture is different:

• Aquarists, as a rule, strive to reduce carbonate hardness to recommended values.
• The surface area is not enough to enrich the volume of water with carbon dioxide.
• Those who specialize in plant breeding are very reluctant to stock fish (especially large ones) and invertebrates.

Accordingly, without an additional source of carbon, the underwater flora will be doomed to its deficiency and problems with development. CO2 supply systems to the aquarium can solve the problem.

Exotic ways

We will not dwell on them in detail, we will only say that they exist. This is the production of CO2 using an electrolyzer, a powder generator, a TPV device, a hydrocarbonate thermoreactor, and other strange devices, the use of which in household aquarium keeping is not only difficult, but also, in the absence of skill, can be dangerous. Similar exotics should perhaps include “dry ice” (solid carbon dioxide) evaporators, which can lead to explosions and frostbite in the wrong hands. Among the industrial exotics, we can note the tablets for saturating water with carbon dioxide. Such tablets usually consist of calcium carbonate and dry organic acid, as well as retardants and mineral additives. When placed in an aquarium (or in a special device - a carbonator installed on the bottom), such tablets gradually dissolve, releasing CO2 into the water. However, it is impossible to control this process, and their effectiveness raises reasonable doubts.

An example of such tablets:

• Tablets for saturating water with carbon dioxide Hobby Sanoplant CO2 100 tablets
• Tablets for saturating water with carbon dioxide Hobby Sanoplant CO2 20 tablets

What remains? Not the cheapest, but the most modern and reliable solution: supplying CO2 from a cylinder...

Optimal concentration of carbon dioxide in aquarium water

The best way to achieve the growth and harmonious development of aquarium plants is to ensure a concentration of carbon dioxide corresponding to their natural habitat conditions.

Various sources and aquaculture forums give different limits for CO2 concentrations. Thus, experienced aquarists often talk about concentrations from 7 to 30 mg/l; manufacturers of equipment for aquariums, including CO2 supply systems, prefer to operate with figures from 15 to 40 mg/l. For example, Dennerle recommends maintaining a concentration of 15 -30 mg/l, with an optimal value of 20-25 mg/l.

Arend van den Nieuwenhuizen

Aquascaper

There is a general estimate of the lower permissible concentration limit. It must be at least 3 mg/l, otherwise aquatic plants will experience real hunger.

— Arend van den Nieuwenhuizen Aquascaper

Estimating the upper limit is somewhat more difficult. Usually, they take into account the fact that the CO2 content in water is strictly related to carbonate hardness (kH) and acidity (pH). It allows you to calculate the concentration of carbon dioxide using kH and pH. But the inverse relationship is also true - an increase in carbon dioxide content leads to an increase in hardness and a decrease in pH.

Accordingly, when artificially supplying gas to an aquarium, it is possible to change the water parameters, which will put aquatic organisms in danger. With an initial value of kH of about 4 degrees and a neutral reaction, CO2 concentrations as high as 30 mg/l can become dangerous for fish and invertebrates; however, a high hardness index and low pH will not add health to the aquarium flora.

There is a concept called "carbonate buffer". The essence of the phenomenon is that at high kH levels, a large concentration of carbon dioxide is required to seriously increase pH. Accordingly, in harder water the CO2 content can be higher without irreversible consequences for the aquarium inhabitants.

Permissible concentration levels

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

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

The indicator depends on the volume of the aquarium, but at the same time it obeys a law under which its average value can be derived. It is equal to 2-10 milligrams per liter. For standing reservoirs, values ​​of 30 may be normal, but everything is too individual.

First of all, you need to know in what conditions the plants that were planted lived. If their usual state is a mild or almost absent flow, then you can add more carbon dioxide and not be afraid of overconsumption. If they appear only in water areas with a noticeable current, then you can reduce the dose and nothing bad will happen.

The minimum acceptable value is 3-5 milligrams, so the normal level for home use is 1 mg, which is unacceptable.

It is necessary to monitor the level of CO2, since oversaturation can lead to oxygen starvation of aquarium fish.

The importance of balance

Caring only about the optimal concentration of carbon dioxide in water is clearly not enough to ensure stable growth and development of aquarium plants. The other factors mentioned above – light and nutrient availability – should also be kept in mind.

The ambient lighting of the aquarium also affects the CO2 balance in the aquarium

So experts consider the following parameters to be sufficient for stable, although not rapid growth of aquarium flora (given for a water column of 0.4-0.5 m):

• Carbon dioxide concentration 5-7 mg/l;

• Illumination – 0.4-0.6 W/l.

In this case, there are sufficient nutrients resulting from the vital activity of nitrifying microorganisms and hydrobionts.

When the CO2 content increases to 15-20 mg/l, it will be necessary to increase the illumination to a level of 0.7-0.8 W/l. It will be necessary to introduce nutrients, primarily nitrogen. The need for fertilizing with phosphorus and potassium should be checked using aquarium tests.

The aquarium owner should remember that it is in conditions of balance that higher aquatic plants demonstrate their full effectiveness and win in the competition. Their rapid development suppresses algae, which end up on a starvation diet; the aquarium looks clean and healthy.

But as soon as the balance is disrupted, simple ancient algae (thread, “Blackbeard”), more adapted to difficult conditions, gain the upper hand. Their growth provokes further deterioration of the situation.

Gas spray devices

A generating plant would not be complete without a CO2 atomizer. The following is used as a spraying device:

1. Rowan branches. Promote the formation of small bubbles. But they need to be changed frequently due to contamination.
2. Pebbles. They create large bubbles, so not the best option.
3. Bell-shaped caps that retain carbon dioxide.
4. A glass diffuser is the best option if a soda solution of citric acid is used as a reagent.
5. A labyrinth ladder along which carbon dioxide bubbles move, gradually releasing.

Monitoring CO2 concentration in the aquarium

The most accurate and effective method for monitoring CO2 levels is to measure carbonate hardness and pH. It was said above that the concentration of carbon dioxide in water is closely related to these indicators. The values ​​at different pH and kH are tabulated. The optimal content of 15-30 mg/l is highlighted in green.

The main advantages of this method:

• Accuracy of determination of carbon dioxide concentration;

• Efficiency of control.

Many, even quite experienced aquarists, prefer simpler methods:

• 
  Using drop checkers

Such an indicator is a small-sized vessel filled with a special composition (usually water with kH=4 and a chemical acidity indicator pH). The vessel is immersed in the aquarium, the solution comes into contact with water and changes color depending on the CO2 content.

The advantage of the method is its simplicity; the disadvantages are limited operating time (but the indicator liquid can be refilled) and inertia (it takes from 0.5 to 2 hours to change the color of the drop checker). Many test indicators, which are easy to find in pet stores, work on the same principle.

• 
  Counting gas bubbles coming from the system

A bubble counter is built into the lines from the system to the aquarium - a transparent vessel filled with water, in which it is convenient to observe the release of gas. . The fastest way possible - allows you to evaluate the concentration of CO2 during supply, even before it is dissolved in water.

It is believed that 1 bubble per minute per 10 liters of aquarium volume corresponds to a CO2 content of 7-19 mg/l. Of course, the accuracy of the control is low, but it is quite possible to assess the concentration and prevent exceeding the standards.

• Piercing intensity.

The intensity of oxygen release by plants also directly depends on the concentration of carbon dioxide. Many experienced aquarium owners can estimate the indicator quite accurately by eye based on the “bubbling” of plants and the chemical composition of the water.

Where to get CO2 from?

So, from all of the above, we understood that since CO2 is so necessary in the aquarium, and the fish do not produce enough of it, then it should be supplied forcibly. But where to get it from? There are many options. If you have a small aquarium of 10-30 liters, and you are near it most of the day, then you do not need any CO2 generator at all: in such a jar it is enough to carefully pour a 20 ml glass of ordinary drinking water into the aquarium 2-3 times a day sparkling water from a bottle (of course, not sweet, not salty or mineral). It’s better to take the cheapest one, which is made from tap water - it’s guaranteed to have no harmful additives. If you have a larger aquarium, you will need a carbon dioxide generator, fittings for supplying it, a bubble counter and a reactor that ensures its dissolution in water at the required concentration. Let's start with generators.

Generator options

Fermentation (“mash”)

The simplest method in which carbon dioxide is produced by the breakdown of sugars by yeast cultures. In this case, the generator is any container filled with a nutrient solution and a colony of yeast.

Such a device is easy to make with your own hands; the components for it are available and cheap. The disadvantages of the method include a limited period of action, difficulty in adjustment, and uneven gas formation. Despite this, some manufacturers offer serial “eco” options using this method.

Balloon

In such a system, the gas source is a liquefied CO2 cylinder. The most complex option requires a fitting assembly with a reducer to reduce pressure and pressure gauges to control the pressure in the cylinder and line. But from the point of view of adjustment and control, it is superior to any other method - an electromagnetic and controlled needle valve easily solves all problems.

Chemical

The method is based on the release of carbon dioxide during the reaction of salts (carbonates, for example, soda or limestone) with acids. Requires more expensive parts for the reaction, but can provide fairly long generation (when solving the problem of component dosage). It also has problems with regulation and uneven gas release.

Exotic options

There are many ways to produce carbon dioxide:

• Chemical compounds that emit gas when in contact with water are available in the form of tablets for aquariums.
• Electrolytic, very interesting from the point of view of application, but has a serious problem with the release of hydrogen.

• Use of “dry ice” (problem with dosage and placement of the gas source in the aquarium).
• Sparkling water, etc.

Most exotic methods have not yet found industrial implementation, but they work quite successfully in various homemade products.

Reactors

The reactor must ensure effective dissolution of the gas in the aquarium water. In practice, 2 types are used.

Passive

Dissolution occurs naturally when the gas comes into contact with water.

1-Diffuser. 2-Bell, 3-Ladder

Options for such reactors:

• Diffuser . A device with micro-holes through which gas is forced into the water. Due to the small size of the bubbles, effective dissolution is ensured. It can use both industrial materials (diaphragms) with micropores and natural ones (for example, rowan, linden and some other types of wood).

• Bell . It is a vessel turned upside down, immersed in water. Gas collects in it and dissolves at the border with water.
• "Ladder" , "Labyrinth". A submersible reactor in which the path of a gas bubble to the surface is artificially increased due to a complex configuration. As a result, CO2 has time to dissolve naturally.

Active reactors (pumps)

In such devices, a counterflow of water and gas is created in the working space, which leads to the active dissolution of bubbles. The most complex system in terms of technical implementation, but the best option for large-volume aquariums.

CO2 reactors, atomizers and diffusers

So, the method of generating CO2 has been chosen (I hope that it is still a cylinder and not a “fermenter”!), accessories have been selected, and the final touch remains - how to supply CO2 to the aquarium so that it dissolves in the water and does not erode from it into room? Of course, conventional sprayers, with which we aerate water, are absolutely not suitable! With their help, we will saturate with gas not the aquarium, but the room in which it stands. You need special devices, which in the aquarium industry are called the collective term “CO2 reactors”. Let's start with the simplest ones.

"Bell" or "inverted cup" . Actually, what it is is clear from the name. Usually this is a small plastic or glass container that is filled with water, placed in the aquarium with the open side down (attached to the wall using a suction cup) and filled with gas from a cylinder. During daylight hours, the gas from the cup gradually dissolves and is consumed, and in the evening the cup is filled again with water so that the operation can be repeated in the morning. This CO2 reactor is only suitable for the smallest nano-aquariums, because... its effectiveness is low. The main advantage of the “bell” is that with its help it is impossible to “overdo it” and create a CO2 concentration in the container that is dangerous for fish.

Diffuser ADA Wood

Wooden diffuser - a diffuser of deciduous wood (usually rowan, birch, willow or linden are used). Such a diffuser (unlike a conventional air spray) creates tiny gas bubbles that facilitate its dissolution. The advantage of such sprayers is simplicity combined with significant efficiency. Disadvantages are the need to supply gas under fairly high pressure (otherwise it is difficult to “push” such a stick), variable performance (the wood gradually swells and deteriorates) and fragility (replacement is needed every 2-3 months). You can make such a diffuser yourself, or you can buy a ready-made one:

Glass ceramic and membrane diffusers

This is the most common and diverse type of reactor for dissolving CO2. What unites them all is the principle of operation: gas is supplied to a glass container located under water, the upper part of which is closed with a semi-permeable microporous glass disk, ceramic plate or plastic membrane. There are tiny holes in its surface through which the gas is slowly slowly pressed into the water in the form of tiny bubbles. The supply pressure is regulated in such a way that there are few gas bubbles (and not as in the figure on the left!), and they would not reach the surface of the water, dissolving completely in its thickness.

Diffusers:

• ADA Pollen Glass Beetle 30
• Dennerle Pfeife Mini
• Dennerle Pfeife Maxi

• ADA Pollen Glass Mini
• ADA Pollen Glass Large
• Dennerle Topf Mini

Another type of reactor is the so-called “ bubble ladder ”. These are glass or plastic transparent labyrinths in which each CO2 bubble, launched from below, gradually rises along steps or in a spiral, slowly passing through the water column and dissolving in it along the way. With the correct setting of the “ladder”, not a single bubble should reach its last step, or it should reach so small that it has no chance of reaching the surface of the water. This thing may be bulky, but it usually doesn’t need decoration, because... Just watching the bubbles rising through the labyrinth is a truly meditative sight! There are a great variety of these ladders available, in different shapes and sizes. Their advantage is not only the mesmerizing slow dance of bubbles, but also the fact that they (unlike wooden and membrane diffusers) do not require excess gas pressure, which allows them to be used together with “mash” type generators. They also do not need a separate bubble counter - they can be easily counted with a stopwatch at the entrance to the reactor.

Video 1

Additional devices

In addition to the generator and reactor, the system may need:

• Shut-off solenoid valve . Used to supply gas on time, adjust concentration.
• Check valve . Prevents “sucking” of water, which can lead to component failure, from the aquarium into the system.

• Bubble counter to monitor system performance and CO2 concentration.
• Prefilter , relevant for a “mash” or a chemical generator, especially one assembled with your own hands.

Batch production systems for CO2 supply

Manufacturers of aquarium equipment offer many models of CO2 supply systems. Below is a brief description of the products of some of them.

Dennerle

The company offers CO2 supply systems of various levels, using different technologies for aquariums of any size.

Thus, the Einweg 300 Space balloon system for a 300 liter aquarium is supplied with:

• Replaceable 500 g carbon dioxide cylinder.
• Reducer with built-in solenoid valve.
• Check valve.

• Flipper diffuser with removal of false gases.
• Connecting hose.
• Indicator and tests.

The kit for Nano nano-aquariums is equipped almost similarly, but the container capacity is only 80 g, and a gearbox of the simplest design is used.

To build more complex systems, it is possible to replace components (for example, adding a pressure gauge unit, installing a night shut-off valve, timer, etc.).

The manufacturer also offers BIO systems (for example, BIO 60), in which a balloon with gel and a starting capsule is used as a generator to initiate the process, and a bubble counter is installed.

Eheim

The manufacturer from Germany offers balloon systems for aquariums of almost any size.

The standard set includes:

• A cylinder with liquefied carbon dioxide with (for some, for example 2000 g) the possibility of refueling. Capacity – from 200 to 2000+ g.
• Reducer for reducing pressure (for refueling ones - with a fitting assembly for refueling).
• Bubble counter.
• Diffuser.
• Hose.
• Drop checker and tests.

If necessary, the system can be equipped with electromagnetic and check valves, control devices (timer). Both components from the company and accessories from other manufacturers are suitable (selection required).

Ista

Ista produces high-quality professional-grade CO2 cylinder systems and accessories for them.

The basic system is equipped with:

• Aluminum cylinder with a capacity of 1 liter.
• Reducer with 2 pressure gauges, built-in solenoid valve.
• Bubble counter with check valve.
• Compact diffuser.
• With a hose.

If necessary, the system can be supplemented with control devices (timer, gas concentration controller), an atomizer (external reactor to improve CO2 dissolution).

Aqua

The Russian company offers cylinder systems both in the form of a designer (Standard and Standard+, Profi) and complete ones.

The buyer can choose systems by:

• cylinder capacity;
• gearbox designs;
• diffuser option;
• presence of a bubble counter;
• drop checker options, etc.

CO2 cylinder installation for an aquarium.

For large-volume aquariums, the most optimal method of supplying CO2 is carbon dioxide from a cylinder installation. The CO2 cylinder supply system consists of a cylinder and a control system, which includes: a reducer (1), an electromagnetic valve (2), a fitting (3), a coil with a connector (4) that ensures the operation of the electromagnetic valve, a pneumatic throttle (5) for fine adjustment of the tempo CO2 supply, power supply (6). You can assemble such an installation yourself. But there are also ready-to-use installations on sale, although they are several times more expensive.

Advantages of the method:

• cost-effectiveness in the long term;
• large supply of CO2;
• full control of CO2 supply intensity;
• stability of CO2 supply;
• possibility of automation (by connecting a pH controller).

Disadvantages of the method:

• difficulty of assembly;
• high cost of equipment;
• the need to work with a high pressure cylinder.

Often asked

Why is it not recommended to carry out aeration and CO2 injection at the same time?

Carbon dioxide dissolved in water is easily released, especially with intense movement of water masses. Accordingly, during aeration its concentration can seriously decrease, which will require high flow rates.

Why is it recommended to equip CO2 supply systems with timers?

It is best to supply carbon dioxide to the aquarium during the daytime, while the plants are photosynthesizing. At night, it is not needed and can lead to excess carbon dioxide concentration and a drop in pH. To prevent this, it is recommended to start feeding 1 hour before the start of daylight and end 1 hour before the end. The timer-solenoid valve combination copes with this task perfectly.

Why do factory BIO generators use gel and not a nutrient solution?

The gel allows you to stabilize the reaction rate and extend the operating time of the generator. The same purpose is served in home-made fermentation generators by adding thickeners, such as gelatin or starch.

Why use prefilters?

In fermentation (even serial) or chemical generators, it is possible for harmful substances (acids, alcohol, etc.) to be captured by the gas flow. To prevent them from entering the aquarium, a prefilter is used to purify the gas.

Which reactor is better - active or passive?

The choice should not be based on the type of reactor, but on the ability to completely dissolve the amount of CO2 required for the aquarium. If the reactor copes with this task for a volume of water, there is no point in saying which type is better.

Chemical method

Kipp apparatus

The second method of obtaining CO2 is much less common in the aquarium hobby. It is based on a chemical reaction between bicarbonates or carbonates (baking soda, lime, potash, chalk, marble, eggshells, dolomite, etc.) and acids (acetic, hydrochloric, citric, etc.), in which carbon dioxide. In order to control the reaction rate and the volume of CO2 released, the process is usually carried out in a rather complex unit called the “ Kipp apparatus ” (its classic laboratory version is shown in the figure), in which the reaction between solid carbonate and liquid acid can be finely controlled. The advantages of the method are the low cost of the starting components. The disadvantages are generally the same as those of the fermentation method: the difficulty of adjusting the process, the need to periodically change reagents (lime and acid are consumed), as well as the need for the same protective devices - a Drexel flask and a check valve - because chemical CO2 is also capable of carrying away traces of acid and other harmful components, and the return of aquarium water into the device can damage it.