Every aquarist needs to understand that plants are 40-50% carbon [C] (dry weight), and there is so little of it in an aquarium without CO2 * that they simply have nowhere to get basic building material for your cells! This is clearly seen in the Table of Plant Composition.

Plants use light energy, oxygen, carbon and hydrogen to carry out photosynthesis.
With the help of photosynthesis, carbohydrates, such as glucose, are obtained from carbon dioxide CO2 by the reaction:

CO2 + 6 H2O + 674.000 cal ---> C6H12O6 + 6H2O
or CO2 + 2H2O -> + O2 + H2O

As you can see it impossible without enough CO2.
This formula also shows that plant photosynthesis requires a certain level of light energy (~ 674,000 cal). If the light is not bright enough, photosynthesis will not take place. When the light level is close to optimal **, photosynthesis will occur faster and faster.

Research data (1994) by Tropica (), the largest aquarium plant growing company, showed that in nature, with sufficient nutrients, CO2 + light are the main limiting factors for plant growth. Provided the water was saturated with all the nutrients, Tropica observed the results of growing Riccia for two weeks, and the following results were obtained:
- no CO2 supply + low light - plant growth = 0 (almost no increase in leaf mass in two weeks)
- at low CO2 supply + low light, the growth increases by 4 times (due to the low compensation point, LCP in aquatic plants)
- low supply of CO2 + high illumination, the growth is increased by 6 times.
- with strong light + high CO2 supply, 1 gram of Riccia will grow 6.9 grams, this gives a daily weight gain of 9.2%! (see graph)

If we apply a lot of CO2 at a low light intensity, we will get very little increase in plant growth (green line), as with an increase in light alone (blue line). But under strong light and high concentration of CO2 in water (~ 15-25mg / l), the effect is simply amazing (red line). At light intensities below the Light Compensation Point (LCP), plant growth stops and the light energy is only sufficient to keep the plant alive (yellow line).

Even an average CO2 supply in a poorly lit aquarium results in a 4-fold increase in plant growth, because more chlorophyll can be produced without fatal consequences for the energy balance of the plant - the plant uses less energy and resources to extract CO2 from the water, and more energy remains for optimization of the processing of light energy in plant tissue. As a result, although the light intensity has not been increased, the plant can make better use of the light it already has. Obviously, the benefit of increasing the light intensity + CO2 supply outweighs the effect of increasing only one of them.
This graph confirms the truth that each photon, regardless of the angle of incidence on the plant leaf, is used for the photosynthesis reaction, i.e. the use of CO2 molecules in this reaction directly depends on the light intensity.
Note: Getting maximum growth is one thing, Stability is another.

From the above facts, it follows that: the intensity of the illumination should correspond the amount of CO2 supplied to the aquarium and vice versa.

If the lighting in the aquarium is dim, still aim for a CO2 concentration of at least 15 mg / l (this is small innings)! Better yet, always maintain ~ 30mg / L.

The vast majority of plant lovers who do not know the correct method have a lack of light and no supply of CO2, so the growth rates of plants correspond to the yellow line, at best green... By increasing only the light, you will improve growth and gain blue line, but in this case there is a threat of the appearance of algae. And only by bringing the illumination back to normal and making the supply of CO2, the growth acceleration will be several times ( Red line)! This will cause the plants to grow at an unprecedented rate.
Why is this needed? Firstly, you will not wait several months for the composition to acquire the planned form - this will happen in just 1.5-3 months; secondly, it makes it possible to often prune plants and precisely shape the composition; thirdly, only sufficiently young leaves of aquatic plants have an ideal condition and, accordingly, an ideal appearance. Only with very rapid plant growth can a perfect aquarium, like the works of Takashi Amano, be obtained.

why exactly co2?
Carbon is available to plants in two forms: gaseous as carbon monoxide, and dissolved in water as bicarbonate. Plants prefer to consume CO2 not from bicarbonate, but as pure CO2 without high energy costs, in addition, many plants cannot directly utilize bicarbonate for photosynthesis. Dissolved carbon monoxide (CO2 - carbon dioxide) in water gives plants the best and most easily assimilated carbon source.

what concentration of co2 do plants need?
Carbon monoxide CO2 is highly soluble in water. The CO2 concentration in water and air is equalized at 0.5mg / l. Unfortunately, CO2 dissolves in water ten thousand times slower than in air. This problem is solved by the relatively thick unstirrable layer (Prandtl boundary) that surrounds the leaves of aquatic plants. The immovable layer of aquatic plants is a layer of still water through which gases and nutrients must diffuse in order to reach the plant leaves. Its thickness is about 0.5mm, which is ten times thicker than for terrestrial plants.
As a consequence of this, to ensure optimal photosynthesis of aquatic plants, the concentration of free CO2 in water should be of the order of 15-30 mg / l, however, the maximum permissible concentration of CO2 for fish of 30mg / l must not be exceeded.
The low solubility of CO2 in water, the relatively thick immovable layer and the high concentration of CO2 required to support photosynthesis prompted one scientist to say: "For freshwater plants, the natural level of carbon compounds in water is the main limiting factor in photosynthesis ..." (for more details, see optimal saturation water CO2 and)
Note: ADA, using a diffuser and switching off CO2 at night, delivers carbon dioxide to significantly higher values, although due to intensive consumption by plants, the concentration in the water will not exceed 30mg / l. The resulting mist of fine bubbles produces gaseous CO2, which greatly accelerates plant growth.

co2 and oxygen
Contrary to popular belief, carbon dioxide does not displace oxygen *** from the water and does not limit its availability for breathing of fish - they coexist successfully. On the contrary, due to good plant growth, the oxygen concentration in the daytime, when the plants are actively photosynthesizing, reaches 11 mg / l, which is much higher than 100% of the saturation limit at a water temperature of 24C, and by morning it drops only to 8.0 mg / l. For the normal life of fish, a concentration of dissolved oxygen in water of 5 mg / l (saturation 60%) is sufficient. In fact, in an aquarium with plants, the quality of the environment is so much higher than in a regular aquarium that the fish will be in much better shape, and most species will reproduce without any stimulation to spawn, and the fry grow well in the general aquarium (if the food that reproduces is suitable for them in the general aquarium, small cyclops, etc.). With a CO2 supply and a pH of 7.2-7.5, even keeping Malawian cichlids gives excellent results with regular breeding in a community aquarium.

co2 shutdown at night
When it comes to the question of turning off the CO2 supply at night or not, there are two opinions. Some sources claim that this is not necessary. It is believed that if there is normally buffered water in an aquarium up to 1200 liters (with dKH = 2-4), and it is not overpopulated with fish, the oxygen content by the morning remains high enough (8 mg / l), and the pH is more or less stable. The use of ADA CO2 supply with a diffuser has its own peculiarities, it allows you to turn off the gas supply at night without fear, and gives an unexpectedly good effect!
Plants consume CO2 only during photosynthesis, so the gas supply at night is simply not needed. Maximum photosynthesis occurs in the morning when there is a lot of free CO2 in the water, and the level of O2 and solar irradiation is the most low[cm. ], therefore it is important in the morning before turning on the light to saturate the water with carbon dioxide by turning on the CO2 supply 1-2 hours BEFORE turning on the light. With the Step lighting method, the Rubisco activity is much higher and the demand for CO2 in the morning is lower than with a uniform one and CO2 consumption is more efficient, therefore, it is not necessary to turn on the CO2 supply 1-2 hours before turning on the light. [see, section Metabolic flexibility]
Usually the choice is made based on personal preference. If CO2 is supplied by spraying at night, it is turned off, but if by dissolution (into a canister filter), then it is not, allowing you to save on a glass diffuser and remove one device from the aquarium, significantly reduce gas consumption, and make system maintenance easier. Spraying can produce a slightly better plant appearance and is very good at removing suspended matter from the water. In any case, one of the decisive factors for the stability of the aquarium is the stability of the CO2 supply. Both options work well.

balance of light and co2
Lighting intensity and CO2 supply must match.

Tropica research confirms what Takashi Amano said to the Aqua Journal: "The watts of light must match the amount of CO2 supplied. If the light is too intense and the plants are not getting enough CO2, strong light will do more harm than good."

also says that too much light without the proper supply of CO2 is only harmful to the plants. Plants do not always need a lot of CO2 for photosynthesis, which can be seen from the photosynthesis formula: 6 CO2 + 12 H2O -> C6H12O6 + 6 H2O. At the same time, plants can release oxygen (actively photosynthesize) even WITHOUT the intake of nutrients! This cannot last long. Plants become weaker and weaker despite active photosynthesis. At the same time, their consumption of phosphates and nitrogen from water decreases, and algae will immediately take advantage of this.

If there is a lot of light but not enough CO2, plants will not grow actively and algae will appear. Injected liquid fertilizers (such as PMDD) will further exacerbate the problem. On the other hand, if there is not enough light and a lot of CO2 is supplied, the plants do not consume CO2 and its concentration can exceed the permissible limit and become toxic to fish and invertebrates (> 30mg / l). Some plants are more light-loving than others, such as long-stemmed plants with very thin leaves. As they require more light, they also require more CO2! As Takashi Amano says, there are no complex and simple plants, there are simply light-loving and shade-loving ones - except for the different required amount of light and CO2, they are no different. The power of the fluorescent lamps and the supply of CO2 should be determined from the very beginning of the creation of the NA, so that later these factors do not reduce the growth of plants - it will be easier to determine their need for other nutrients. [Cm. Ole Pedersen, Claus Christensen and Troels Andersen, 1994 www.tropica.com.]

how much to serve co2

How to make pH and saturation CO2 water ideal for plants? Make KH = min. 4 degrees in the aquarium, and adjust the CO2 supply so that the pH is set at 6.8 in the morning and 7.2 in the evening - as a result, the average CO2 concentration will be ~ 15-30mg / l.

pH and KH are something that anyone running a plant aquarium absolutely needs to understand. These are two interrelated concepts.
pH is a measure of the acidity of water(acidity). It is determined by the negative logarithm of the amount of hydroxide ions (H +) in water - the more there are, the lower the pH. The pH reaction of water can be acidic (less than 7.0), neutral (pH = 7.0) or alkaline (pH> 7.0).
Carbonate hardness kN (i.e. carbonate hardness) is a measure of the alkalinity of water. KH indicates the ability to maintain pH at a certain level, that is, it is an indicator of the buffering properties of water... She is constantly changing, which is why she is called temporary stiffness... The KH value is the amount of bicarbonate in the water, which neutralizes the acid that is constantly forming in the aquarium to lower the pH, thereby keeping the pH from dropping.

In nature, the concentration of CO2 in water is rarely as high as required by an underwater garden, but in natural reservoirs the ratio of the surface of water through which CO2 is absorbed to the mass of plants is incomparably greater than in an aquarium, and its reserves are constantly renewed by flow and discharge from bottom sediments. Without artificial enrichment of the water with CO2, all the carbon dioxide available in the aquarium will be used by the plants in the first hour or two after the lights are turned on and growth will stop.

In practice, the feed rate can be determined as follows (at 100% reactor efficiency):
at kH = 2-4, the flow should be 1 bubble per minute for every 10 liters of water in the aquarium. This will give CO2 = 7-19mg / L at pH = 6.8-7.2.
How to use a much larger feed was discussed ¬.

These recommendations are only indicative. safe framework CO2 supply. The most efficient way to deliver CO2 is by atomization. This can be done using a glass diffuser, a pump diffuser, or a Tom Barr reactor.

influence co2 on pH

co2 lowers pH
When CO2 is supplied to the aquarium, small amounts of carbonic acid (0.1-0.2%) are formed in the water, it dissociates into ion and bicarbonate (KH base), the concentration of H + ions increases, lowering the pH - this means that by supplying CO2 we can lower the pH in the aquarium simultaneously giving the most important plant growth nutrient carbon [C].
As the pH of the water decreases, the proportion of carbon in the form of CO2 increases; dissolved CO2 becomes higher in water than bicarbonates. (see below under "pH") Since the pH value is influenced by the carbonate buffer KH and the CO2 concentration in the water, relationship (pH<->KH<->dissolved CO2) is hard... Since the pH is mainly determined by the presence of the KH carbonate buffer, the amount of CO2 supplied depends on how we want the pH level in the aquarium with plants. That is, in the triple (pH - KH - CO2), pH and KH are given values, and the CO2 supply will be regulated to ensure both the optimal pH level = 6.8-7.2 and the concentration of carbon dioxide in the water. To obtain the optimal concentration of CO2 = 15-30mg / l and pH = 6.8-7.2, the water should be with the initial KH = 2-8, which corresponds to water with a total hardness of dGH = 4-10.

but what should be kH and pH?

pH

Optimal for plant growth is pH = 6.8-7.2. Why exactly 6.8-7.2?

Plants need a lot of CO2 .
A lot of CO2 is needed for good plant growth. As stated earlier, CO2 is the best carbon source for plants. But in water, carbon can exist in two forms: carbon dioxide CO2 dissolved in water, and bicarbonate. CO2 gas dissolved in water is directly absorbed by ratios by diffusion through the cell walls. Bicarbonate contains chemically bound CO2 - that is, NOT available for direct consumption by plants - they must first absorb HCO3- and then extract CO2 inside the cells. This is a complex and energy-intensive process, and not far from all plants can do it (more details).

In soft and acidic water with pH<7.0 большинство углерода (~70%) будет находится в виде CO2 прекрасно усваиваемого растениями, и только 30% в виде бикарбоната , то есть: the lower the pH, the more carbon is in a form readily available to plants - dissolved in water gaseous CO2! This suggests that when equal By supplying CO2 in a soft water aquarium with KH = 2-6 (dGH = 4-6 °), the plants receive more CO2 than in a harder water aquarium.

PH stability during biological processes in the aquarium.
Buffering is the result of the chemical properties of weak acids. When a weak acid dissociates in water, the ratio of acid-base pairs formed has a logarithmic ratio. If we print out a graph of the acid-bace ratio versus pH, we can see that above or below a certain pH value, the curve is almost flat, that is, when acids or bases are added to the water, the pH will not change significantly! At a specific pH called equilibrium point, the curve is practically flat, meaning that the addition of acids and bases will change the pH very little. Note that there can be more than one equilibrium point, and they are different for different acids.
We are interested in carbonic acid, equilibrium point of which pH = 6.37... it ideal value for aquarium plants, as the desired pH level is slightly above this value and usually tends to decrease because in the aquarium nitrification process consumes a lot of alkaline buffer - bicarbonate HCO3-. Since the initial pH level is ABOVE the equilibrium point and any displacement will be towards it, quite a lot of acid can be "buffered" before the pH drops below this point. This is the key to pH stability, and this is the pH (6.6-7.2) chosen by T. Amano as optimal for Nature Aquarium.
Note: Krause's method of determining the optimal water pH for a particular aquarium may be based on this phenomenon.

The ratio of ammonium NH4 + and toxic ammonia NH3.
ammonium can also exist in the form of ammonia, which is very toxic to all living things (toxic even at a concentration of 0.06 mg / l). The ammonium NH4 + / ammonia NH3 ratio in an aquarium is mainly dependent on the pH value. The lower the pH, the less toxic ammonia. At pH = 7.0, it is only 0.5%, but when the pH rises to 7.5, ammonia is already 4%. That is eight times more! A simple rule of thumb: Above pH 7.0, the proportion of toxic ammonia begins to increase significantly. At pH = 6.8-7.2, the proportion of toxic ammonia in NA will be in the range of 0.4-0.8%. Since NA is kept at a very low level of ammonium / ammonia, even if the situation worsens, a pH in the range of 6.8-7.2 guarantees the absence of toxic ammonia.

Activity of nitrifying bacteria.
At pH = 6.6, the nitrifying activity of bacteria is approximately 85% of the maximum level. This means that in NA at pH = 6.8-7.2 the bacteria never work at maximum, and with a slight deterioration in water parameters, they can always slightly increase the activity and cope with the increased load, while maintaining the stability of the aquarium. This creates the same stability margin as in the above example with the pH equilibrium point. (Nitrification occurs most actively at pH = 7.5-8.5; below pH7.5 it slows down.)

KH

Now you need to determine what should be the value of KH. We have found that in an aquarium for optimal plant growth, you need to maintain a pH of 6.8-7.2.

Soft water with kH = 2-5 is acidic in itself and is also buffered at pH = 6.0-7.3 because most of the carbon in it is contained in the form of carbon dioxide and not carbonic acid. This means that in order to avoid a drop in pH below normal when supplying carbon dioxide, the minimum kH level before CO2 is supplied to the aquarium should be min.KH = 4.0.

Why not more? Because if the initial level kHmax.> 7.0, i.e. the water is too hard, it will have an initial pH of ~ 7.8, and in order to reach the desired pH level, it will be necessary to exceed the maximum allowable CO2 concentration for fish of 30mg / l. In this case, it simply will not be possible to lower the pH to the optimal level.
If KH is too low (kH<2), при завышенной подаче CO2 или повышении уровня нитратов возникнет угроза внезапного sharp pH drops below 6.8 (the so-called pH collapse), which is detrimental to plants and fish.

To maintain a stable pH, the water must have a minimum level kHmin. = 4 so that at any moment the carbonate buffer of water is not depleted, and this does not lead to a collapse of pH. There is another way to avoid this - a substrate with good buffering properties that will buffer the pH due to alkalinity not kH.

Further. Remember that the relationship (pH - kH - CO2) is tough, which means that according to Table 1 of the dependence of one value on another, according to the required pH and a given KH, it is possible to determine what the CO2 concentration will be at the chosen kH and pH.

The table shows that at pH = 6.8-7.2 and KH = 4-5, the CO2 concentration will be 7.6-23.8 mg / l. By feeding this amount of CO2 into the water at KH = 4-5, we will obtain both the optimal pH and the optimal saturation of the water with CO2 for the vigorous growth of plants in the aquarium.

The lower the pH (<7.0), тем больше в воде легко потребляемого растениями dissolved CO2, and the better the intake of all other nutrients by the plants. At the same time, kH is not at all important for plants, pH is important. Often the value of kH is equal to dH, but sometimes it is not. The water hardness dH is not a significant factor and is of minor importance in a plant aquarium. A high GH does not inhibit plant growth at all, often even long-stemmed plants grow in water with a dH of 10-12 better than soft water, and the water should never be too soft to avoid sciatica.

It is important to know that this pH / kH / CO2 relationship is characteristic of only for an aquarium in which the main component of alkalinity is the carbonate hardness of water kH (with neutral soil without organic matter and without plants), in an aquarium with plants, with soil rich in organic matter and humic acids, kH plays a much smaller role in the buffer system, which makes similar tables and pH controllers are useless. The only sure way to control the CO2 concentration is with a drop checker with a calibrated solution kH = 4.00.

do we need kH at all?
An increase in the concentration of CO2 in water causes a decrease in both pH and kH. It was said above that when CO2 is supplied, there must be a certain minimum min.kH level that will not allow the pH acidity to collapse (irreversibly sharply drop) when the CO2 concentration reaches a certain value, which will exhaust the entire kH buffer, that is, pH buffering will stop. The problem is that after such a collapse, after a decrease in CO2 supply, kH will no longer be able to recover. That is, you need an alkaline buffer. This is true, but a plant aquarium can do without kH at all and have enough buffer so that there is no drop in pH.
For example, if we feed CO2 ~ 30mg / L into very soft water, the pH might be 5.8 and kH = 0. Why then does the pH not collapse and is it stable? This is because in the substrate and in water, in addition to kH (carbonate / bicarbonate), there are still pH buffering substances, that is, there is still alkalinity, and alkalinity is far from only carbonant hardness kH ...
The misunderstanding comes from the fact that they confuse the concepts of carbonant hardness kH and alkalinity in general (alkalinity). Alkalinity and kH are not the same thing at all. Alkalinity is the ability of a solution to resist a drop in pH (buffer) when acid is added. The higher the value, the more alkalinity. It is formed by compounds of carbonates, bicarbonates, borates, phosphates, hydroxides. And KH is only a measure of the amount of carbonates / bicarbonates in the water. That is, the measure of alkalinity does not necessarily indicate the presence of any of these compounds, namely carbonates / bicarbonates - kH. Simply put, alkalinity is the ability to hold pH in general, and kH is only a fraction of it - carbonates / bicarbonates. That is, the absence of kH does not mean that the solution does not have an alkaline buffer capacity. KH of water can be 0-1, but when CO2 is supplied ~ 30mg / l there will be no collapse of pH - it will be retained not due to kH, but due to other connections giving alkalinity. Usually kH forms the majority of the alkalinity in the system, but this is not the case in a plant aquarium. In such aquariums, the buffer capacity of the substrate with a high content of humic acids and organics such as ADA Aqua Soil or its analogs maintains the pH value; they are able to do this for several years. Humic acids lower the pH to 6.8 without any CO2 supply, while CO2 supply up to 30mg / L equilibrates the system at pH ~ 6.5. In addition, part of the kH and substrate buffer is constantly renewed with the changeover water.
But if in a buffered alkalinity other than kH at kH = 0, pH acidity does not depend on kH, how then to control the CO2 concentration, because then you cannot use the pH dependence table<->kH? Only with a dropchecker with a calibrated solution KH = 4.00.
Failure to understand these things sometimes leads aquarists to buy the most unnecessary device for a plant aquarium - a pH controller.
As for the well-being of plants, they need a certain pH, and kH they indifferent... KH is not the total hardness of the water dH giving vital elements (Ca, Mg), and it does not affect plant growth in any way, only the optimal pH range of 6.8-7.2 improves their growth. And most fish suitable for a plant aquarium are quite comfortable even with a pH of 5.5. Therefore, we do not need kH, but only if there is another alkaline buffer - in the substrate.

hard water
For the best plant growth, an optimal pH of 6.8-7.2 is required. If the tap water has a KH higher than 7.0dKH, you will not be able to reach the required level because the CO2 concentration will exceed the maximum allowable for fish - 30mg / l. It is necessary to soften the water by mixing with water obtained after filtration by reverse osmosis (KH ~ 0).
A common misconception is to think that when CO2 is applied, the pH drop in hard water will be much greater than in soft water. This is not true. Whether for soft or hard water, when CO2 is supplied, the pH shift will be almost equal, including the daily fluctuations when the CO2 supply is turned off at night. Just look closely at the kH-pH-CO2 table.

soft water
Water that is too soft carries two dangers: the possibility of a pH collapse when CO2 is supplied, and a lack of Ca + Mg. Soft water usually (but not always!) Also has a very low kH. If there is no alkaline buffer in the water, the addition of CO2 can lead to a drop in pH. But since kH is only part of this buffer, whether you need to increase the carbonate hardness of the water, kH depends on what kind of substrate you have. If this is an aquarium with organic-rich plants, the kH need not be increased. In this case, the water hardness is increased by adding only the constituents of the constant water hardness, for example, Amania GH Booster. If you need a high pH + kH (for example, you grow plants in an aquaruim with cichlids), use the Amania GH + KH Booster that increases both GH and kH. You can also mix hard tap water with RO water to obtain water with the required dkH and dH. For increasing the RO water hardness, see the RO water recovery section.

what if the carbonate hardness (KH) is too high?
You can soften water to the required KH = 4 by purifying hard tap water by reverse osmosis and mixing it with tap water.
If the carbonate hardness of the water dKH is much higher than required (> = 7.0), and there is no possibility of softening the water, CO2 should be supplied until a concentration of no more than 30 mg / l (pH ~ 7.0) is reached. It will not work to lower the pH to the optimal value by supplying CO2, since this will require exceeding the permissible CO2 concentration for fish of 30 mg / l, but this can be done using a water acidifying substrate like ADA Aqua Soil. Never use an ion exchange column for this!

Example. In the aquarium, the water BEFORE the CO2 supply was KH = 10. Let's adjust the CO2 supply. Then measure the pH once a day (in the middle of the lighting period of the aquarium), if the pH is above 7.0, gradually increase the supply of carbon dioxide. When the CO2 supply is such that pH = 7.0 this will be the optimal supply of carbon dioxide to your aquarium. Once again measure the KH value slightly decreased from the CO2 supply, and read the CO2 concentration from the table. At kH = 6.0 and pH = 7.0, the CO2 concentration will be 18mg / l, and the pH will be 6.8 in the morning and 7.2 in the evening.

Effect of plant photosynthesis on pH during the day
During the day, the photosynthesis of plants affects the pH of the water in the aquarium. Plants photosynthesize during the day by consuming small amounts of carbonic acid, and the pH rises.
Whether the plant is lit or not, it breathes 24 hours a day. That is, plants are constantly consuming oxygen and producing CO2. Only during the day, while photosynthesizing, plants consume CO2 and produce oxygen as a by-product.
In a densely planted aquarium, the light turns on at 10-00 in the morning, and turns off at 21-00 in the evening. At night, when there is no light, plants breathe for 11 hours, emitting CO2, which lowers the pH, respectively, the pH will drop to 6.8 in the morning. When the lights are turned on in the morning, plants are simultaneously photosynthesizing and breathing, consuming CO2 and releasing oxygen - the pH begins to rise. At noon, the pH will rise to 7.0, and will continue to rise until 9:00 p.m. to 7.2. When the lights are turned off, the pH will start to gradually drop again as the CO2 concentration rises. The more actively the plants grow, the more they consume CO2 during the day, and the more the pH will rise in the evening.
T. Amano says: “To determine how much CO2 is consumed by plants, you can compare the pH level in the morning and in the evening. By turning off the lights after a day of CO2 consumption by the plants and the production of oxygen. The larger this difference, the more CO2 consumption and therefore healthier your plants. " (vectrapoint.com)

Effect of the nitrification process on pH
During the nitrification process, i.e. the process of converting ammonium NH4 + into nitrate NO3 by bacteria, Nitrosomonas bacteria using NH4 + and bicarbonate HCO3- first produce toxic nitrite NO2- and carbonic acid H2CO3, and then Nitrobacter converts nitrite NO2- into harmless nitrate NO3- during which for every 1mg of ammonium conversion, 8 mg of an alkaline buffer, namely bicarbonate HCO3-. At the same time, when the intermediate nitric acid metabolite HNO3 is converted to NO3, H + is released, which lowers the pH. When one NH4 molecule is converted to NO3, two H + ions are released, the simplified process is described as: NH4 + + 2O2 => H2O + H + + H + + NO3- (see Understanding soil analysis data 59p.). More details for NH4-> NO2 by Nitrosomonas bacteria: 55NH4 ++ 76 O2 + 109HCO3- => C5H7O2N + 54NO2- + 57H2O + 104H2CO3; for NO2-> NO3 by Nitrobacter bacteria: 400NO2- + NH4 + + 4H2CO3 + HCO3- + 195 O2 => C5H7O2N + 3H2O + 400 NO3- ().
In an aquarium with plants, both the carbonate kH and the total water hardness GH and the pH decrease over time. With the deterioration of plant growth in water and the state of the bacterial colony in the filter and soil, the nitrification process stops halfway and the accumulation of not only toxic nitrite NO2-, but also bicarbonate HCO3- occurs, as a result of which the pH rises.

co2 weathering
Carbon dioxide very easily escapes from the water into the surrounding air, just as easily as when shaking a bottle of sparkling water, so movement of the surface of the water must be completely eliminated. For this:
- NEVER aerate the water during the day, only at night
- always place the canister filter outlet below the water level,
- do not use a sprinkler to return water to the aquarium from the filter,
- in the case of using pumps to create water movement, position them so as to exclude movement of the water surface.
Never use open hinged filters such as bio-wheel or waterfall filters - they strongly erode carbon dioxide from the water! Some aquascapers use them as well, but it is important how to install it. If you hang it on an aquarium with a frame so that the water falls from a height, then it erodes the CO2, if an aquarium without frames and ties and the spout is submerged, then no.

co2 concentration control
To determine the concentration of CO2 in water, it is enough to measure the KH of water and its pH, and then calculate it using the formula: CO2 = 3.0 * KH (degrees) * 10 ^ (7.00 - pH)... You can also determine from a table or graph, or using a calculator. This method has a large error and cannot serve as an accurate guideline.

thinking that pH and co2 are the same is dangerous
If the pH drop is due to large amounts of CO2 as a result of bacterial respiration in the soil, the CO2 supply can be increased. But if this happens against a background of high nitrate levels, then the low pH is caused by poor biological equilibrium and it is necessary to increase the water change, lower the nitrate, and only then increase the CO2 supply.
Too high a pH is a typical early setup aquarium "disease". T. Amano, in the Algae Control section of the Aqua Journal website, draws attention to this fact:
"... there are not enough bacteria in the early stages and the pH is very high, lower the pH by increasing the CO2 supply." (note: but not earlier than the second week of setup!) In a mature aquarium, there are many bacteria in the soil and in the filter, which means the pH, more CO2 is released, and as a result the pH is lower.

* CO2 concentration of only 2-3 ppm: from the vital activity of nitrifying bacteria decomposing organic matter in the soil and canister filter, respiration of fish and plants
** For calculation of the power of fluorescent lamps for NA, see the lighting section.
*** see the section on the role of oxygen.

Article Ole Pedersen, Claus Christensen and Troels Andersen (2001), 1994 www.tropica.com ();
she's in English. in .pdf format in the online journal: Interactions between CO2 and light stimulate the growth of aquatic plants. ...
from "", by George and Karla Booth, Copyright 2000, www.frii.com/~gbooth/AquaticConcepts/Articles/book.htm#Intro
,
by Dave Hueber t http://www.hallman.org, mailto: [email protected]
Horst, Kaspar, & Kipper, Horst E. (1986). The Optimum Aquarium. Bielefeld, Germany: AD aquadocumenta Verlag GmbH
By Ole Pedersen, Troels Andersen and Claus Christensen, This article first appeared in The 2007 vol. 20 (3) pp 24-33;
Interactions between light and CO2 enhance the growth of Riccia fluitans L .; Andersen T & Pedersen O. (2002); HYDROBIOLOGIA 477: 163-170
Andersen T, Pedersen O (2004) Higher CO2 concentrations alleviate co-limitation of light, N and P on growth in the aquatic liver wort Riccia fluitans L. XXIX SIL Congress. 8-14 August, Lahti, Finland,
by John Whitmarsh, Govindjee
Photosynthesis -
CO2 for Landscaped Aquariums - TFH, 06/00
CO2 Supplementation in thePlanted Tank - TFH, 03/96
at Petfrd.com
, by John LeVasseur
largest pro CO2 (eng.)
""
www.rexgrigg.com -.
, Tom Barr
, Tropica ()
Understanding the General Chemistry of the Planted Aquarium, Gregory Morin, Ph.D, Seachem ()

DEFINITION

Carbon dioxide(carbon dioxide, carbonic anhydride, carbon dioxide) - carbon monoxide (IV).

Formula - CO 2. The molar mass is 44 g / mol.

Chemical properties of carbon dioxide

Carbon dioxide belongs to the class of acidic oxides, i.e. when interacting with water, it forms an acid called carbonic acid. Carbonic acid is chemically unstable and immediately decomposes into its constituents at the moment of formation, i.e. the reaction of interaction of carbon dioxide with water is reversible:

CO 2 + H 2 O ↔ CO 2 × H 2 O (solution) ↔ H 2 CO 3.

When heated, carbon dioxide decomposes into carbon monoxide and oxygen:

2CO 2 = 2CO + O 2.

As with all acidic oxides, carbon dioxide is characterized by interaction reactions with basic oxides (formed only by active metals) and bases:

CaO + CO 2 = CaCO 3;

Al 2 O 3 + 3CO 2 = Al 2 (CO 3) 3;

CO 2 + NaOH (dilute) = NaHCO 3;

CO 2 + 2NaOH (conc) = Na 2 CO 3 + H 2 O.

Carbon dioxide does not support combustion, only active metals burn in it:

CO 2 + 2Mg = C + 2MgO (t);

CO 2 + 2Ca = C + 2CaO (t).

Carbon dioxide reacts with simple substances such as hydrogen and carbon:

CO 2 + 4H 2 = CH 4 + 2H 2 O (t, kat = Cu 2 O);

CO 2 + C = 2CO (t).

When carbon dioxide interacts with active metal peroxides, carbonates are formed and oxygen is released:

2CO 2 + 2Na 2 O 2 = 2Na 2 CO 3 + O 2.

A qualitative reaction to carbon dioxide is the reaction of its interaction with lime water (milk), i.e. with calcium hydroxide, in which a white precipitate is formed - calcium carbonate:

CO 2 + Ca (OH) 2 = CaCO 3 ↓ + H 2 O.

Physical properties of carbon dioxide

Carbon dioxide is a colorless and odorless gaseous substance. Heavier than air. Thermally stable. When compressed and cooled, it easily passes into a liquid and solid state. Carbon dioxide in a solid state of aggregation is called "dry ice" and readily sublimes at room temperature. Carbon dioxide is poorly soluble in water, partially reacts with it. Density - 1.977 g / l.

Obtaining and using carbon dioxide

There are industrial and laboratory methods for producing carbon dioxide. So, in industry it is obtained by calcining limestone (1), and in the laboratory - by the action of strong acids on carbonic acid salts (2):

CaCO 3 = CaO + CO 2 (t) (1);

CaCO 3 + 2HCl = CaCl 2 + CO 2 + H 2 O (2).

Carbon dioxide is used in food (carbonation of lemonade), chemical (temperature control in the production of synthetic fibers), metallurgical (environmental protection, for example, brown gas precipitation) and other industries.

Examples of problem solving

EXAMPLE 1

The problem of exceeding the content of carbon dioxide in indoor air is being discussed more and more often in the last 20 years. New research comes out and new data is published. Are the building codes for the buildings we live and work in keeping up with them?

The well-being and performance of a person is closely related to the quality of the air where he works and rests. And air quality can be determined by the concentration of carbon dioxide CO2.

Why exactly CO2?

• This gas is everywhere where people are.
• The concentration of carbon dioxide in a room directly depends on the processes of human life - after all, we exhale it.
• Excess carbon dioxide levels are harmful to the state of the human body, therefore, it must be monitored.
• An increase in CO2 concentration clearly indicates problems with ventilation.
• The poorer the ventilation, the more pollutants are concentrated in the air. Therefore, an increase in indoor carbon dioxide is a sign that air quality is declining.

In recent years, proposals have appeared in the professional communities of doctors and building designers to revise the methodology for determining air quality and expand the list of measured substances. But so far nothing clearer has been found about the change in CO2 levels.

How do you know if indoor carbon dioxide levels are acceptable? Experts offer lists of standards, and they will be different for buildings of different purposes.

Residential Carbon Dioxide Standards

Designers of apartment buildings and private houses are based on GOST 30494-2011 entitled “Residential and public buildings. Indoor microclimate parameters ". This document considers the level of CO2 optimal for human health to be 800 - 1,000 ppm. The mark at the level of 1,400 ppm is the limit of the permissible content of carbon dioxide in the room. If there is more, the air quality is considered poor.

However, already 1,000 ppm is not recognized as a normal variant by a number of studies devoted to the dependence of the state of the body on the level of CO2. Their data indicate that at around 1,000 ppm, more than half of the subjects feel a deterioration in the microclimate: increased heart rate, headache, fatigue and, of course, the notorious "nothing to breathe".

Physiologists consider 600 - 800 ppm a normal level of CO2.

Although some isolated complaints of stuffiness are possible at the indicated concentration.

It turns out that the building standards for the level of CO2 contradict the conclusions of physiologists. In recent years, it is from the latter that the calls to renew the permissible limits have been heard louder and louder, but so far the calls have not gone further. The lower the CO2 norm, which the builders are guided by, the cheaper it costs. And those who have to solve the problem of ventilation of the apartment on their own have to pay for this.

Carbon dioxide standards in schools

The more carbon dioxide there is in the air, the harder it is to focus and cope with the workload. Knowing this, the US authorities recommend that schools maintain CO2 levels below 600 ppm. In Russia, the mark is slightly higher: the already mentioned GOST considers 800 ppm or less optimal for children's institutions. However, in practice, not only the American but also the Russian recommended level is a dream come true for most schools.

One of ours showed that for more than half of the study time, the amount of carbon dioxide in the air exceeds 1,500 ppm, and sometimes approaches 2,500 ppm! In such conditions it is impossible to concentrate, the ability to perceive information is critically reduced. Other likely symptoms of excess CO2 include hyperventilation, sweating, eye inflammation, nasal congestion, and difficulty breathing.

Why it happens? The offices are rarely ventilated, because an open window means cold children and noise from the street. Even if the school building has powerful central ventilation, it is usually either noisy or outdated. But the windows in most schools are modern - plastic, sealed, airtight. With a class of 25 people in an office with an area of ​​50-60 m2 with a closed window, carbon dioxide in the air jumps by 800 ppm in just half an hour.

Carbon dioxide standards in offices

In offices, the same problems are observed as in schools: the increased concentration of CO2 makes it difficult to concentrate. Errors multiply and labor productivity drops.

The standards for the content of carbon dioxide in the air for offices are generally the same as for apartments and houses: 800 - 1,400 ppm is considered acceptable. However, as we have already found out, already 1,000 ppm causes discomfort to every second person.

Unfortunately, in many offices the problem is not solved in any way. Somewhere they just don't know anything about her, somewhere the management deliberately ignores her, and somewhere they try to solve it with the help of an air conditioner. A jet of cool air really creates a short-term illusion of comfort, but carbon dioxide does not disappear anywhere and continues to do its "dirty deed".

It may also be the case that the office space was built in compliance with all standards, but it is operated with violations. For example, the density of employees is too high. According to building rules, one person should have from 4 to 6.5 m2 of area. If there are more employees, then carbon dioxide accumulates in the air faster.

Conclusions and outputs

The problem with ventilation is most acute in apartments, office buildings and childcare facilities.
There are two reasons for this:

1. Discrepancy between building codes and hygiene guidelines.
The former say: no more than 1,400 ppm CO2, the latter warn: this is too much.

2. Failure to comply with standards in the construction, reconstruction or operation of the building.
The simplest example is the installation of plastic windows that do not allow the outside air to pass through and thereby aggravate the situation with the accumulation of carbon dioxide in the room.

Very often, people who have completed a freediving training course ask how they can train their breath holding at home away from the sea in order to better prepare for the next trip and not lose shape.

Quite an effective and popular training among freedivers, which allows to significantly increase the breath-holding time, is the strategic hold training according to the CO2 and O2 tables. What is it and what is it for?

CO2 table. Hypercapnic table

As is well known, the main trigger for inhalation is the level of carbon dioxide in the lungs. When you hold your breath and increase the amount of carbon dioxide, our brain sends a signal to the respiratory system to breathe. That. breath holding is divided into 2 phases: the phase of comfort and the phase of struggle, when the brain actively sends signals to the respiratory system, and the latter begins to respond to this by contractions of the diaphragm (contractions).

The workout is a series of breath holdings designed to develop a tolerance for increased CO2 levels (hypercapnia) in the body, increasing the level of carbon dioxide during each subsequent hold. To do this, the breath hold time remains constant, and the rest time between holds is gradually reduced, thereby increasing the residual CO2 level for each subsequent hold.

CO2 table example

Table O2. Hypoxic table

A series of breath holdings aimed at developing the body's tolerance to a decrease in oxygen levels (hypoxia). This is achieved by gradually increasing the duration of breath holding with the same rest time. The rest interval should be long enough to get rid of the excess CO2 accumulated after the delay and recover. The delay interval is large enough to obtain the required hypoxic load, i.e. towards the end of the table, the delay should be close to the maximum.

O2 table example

We remind you that all independent training for holding your breath must be carried out only on land! The first rule of freediving - never dive alone, also applies to static breath holding.

For convenience, we recommend using a nose clip and purchasing an oximeter to track and record results. You can create a table in which to record important parameters such as heart rate, blood oxygen saturation, contraction onset time, maximum delay time, etc. This will allow you to analyze your results, see your progress and will create an additional incentive for training.

When holding your breath for a while, one of the important principles is not to think about time. Therefore, for training on tables, it is recommended to use special applications for the phone, in which the necessary training parameters are configured, after which you sit comfortably on the bed, put your phone next to it, and the application tells you all the instructions.

Examples of apps for Android phones: