Fertilizing aquarium plants

Plant fertilization methods: PMDD and EI

The beautiful appearance of a planted aquarium largely depends on additional fertilization of the plants it contains. And just like for humans, the best effects are brought by a balanced diet, similarly in the case of plants their fertilization should be balanced.

Plants absorb various nutrients with different intensity and speed. Contrary to appearances, this does not only depend on the given species, but also is associated with, for example, the growth stage (young plants need more nutrients) or the transition of the plant to the generative period (blooming and producing seeds).

Optimizing fertilization (adding fertilizers "just right", neither too much nor too little) helps to keep plants in excellent condition, and at the same time, it will not strain our budget too much.

There is one rule – more fertilizer does not mean better and faster growth of plants. Scientific research has proven that plants have the ability to absorb only a certain level of individual nutrients. It means that above these values we will not "improve" anything in plants, but we can only harm the aquatic environment. Dosing the sufficient amount of nutrients should be the goal of every aquarist who has plants in his tank.

There are two main methods of plant fertilization in the aquarium: PMDD and EI, which I will try to explain in the next part of this article.

PMDD Fertilizing – Poor Man's Dosing Drops

Introduction

This is a method of fertilizing aquarium plants with all necessary nutrients, but with limited amount of phosphorus, aimed at controlling the amount of algae in the aquarium.

This method was developed in 1996, and its creators are Paul Sears and Kevin Conlin. Initially, the method assumed that phosphates would not be dosed at all (their dosing was completely eliminated), as they are available to plants from the metabolic processes of fish, and their excess affects the unwanted growth of algae. Over time, however, it turned out to be erroneous thinking, especially in the case of aquariums with a large number of plants (planted aquarium, Dutch aquarium, natural aquarium). Then the creators of the method concluded that phosphates must also be dosed, but still in a limited amount.

There are several modifications/variations of this method, which differ in the dosing of individual components and the fertilizer itself. A more popular version of this method was once PPS-Pro (Perpetual Preservation System) and PPP Classic.

Original composition of PMDD fertilizer (without phosphorus dosing):

Compound name	Dose
potassium nitrate	1 teaspoon
potassium sulfate	1 teaspoon
magnesium sulfate	2.5 tablespoons
chelate mix: 7% Fe; 1.3% B; 2% Mn; 0.06% Mo; 0.4% Zn; 0.1% Cu; EDTA; DTPA	1 tablespoon
distilled water	300 ml

Modified composition of PMDD fertilizer (with added phosphates):

fertilizer with macronutrients:

Compound name	Dosage
potassium nitrate	25 [g]
monopotassium phosphate	5,8 [g]
potassium sulfate	11 [g]
magnesium sulfate heptahydrate (epsom salt)	20 [g]
warm distilled water	500 [ml]

fertilizer with microelements:

Compound Name	Dosage
chelate mix: 7% Fe; 1,3% B; 2% Mn; 0,06% Mo; 0,4% Zn; 0,1% Cu; EDTA; DTPA (ready-made products: TNC Trace, Plantex CSM+B, Microplex Chelating Agent-EDTA by Miller)	10 [g]
ascorbic acid (E300)	0,25 [g]
potassium sorbate (E202)	0,1 [g]
warm distilled or RO water	250 [ml]

PMDD Fertilizer Dosing

The method requires daily fertilizer dosing, so that the level of all nutrients is stable and to prevent any nutrient from being depleted.

Fertilizer should always be dosed at the same time of day, preferably just before the lighting is turned on.

Fertilizer dosing depends on:

• the amount of plants (how much bottom surface they occupy),
• the type of plants (how they absorb nutrients - through roots or leaves),
• lighting intensity,
• whether additional CO₂ fertilizing is used.

Dosage for a 100% stocked aquarium (referring to the bottom surface of the aquarium), fairly intense lighting, where additional CO₂ fertilizing is used:

• 2 ml macroelement fertilizer for every 40 l,
• 1 ml microelement fertilizer for every 40 l.

We reduce the dose proportionately in case we: do not use additional CO₂ fertilization, use weaker lighting, have fewer plants and do not perform partial water changes.

The indicator of whether the dosage used is correct will always be the condition of the plants in the aquarium, their growth rate (slow growth - too little or too much fertilizer), the appearance of algae (too much fertilizer), possible appearance of chlorosis on the leaves (too little fertilizer).

Fertilizer dosing can also be controlled by regularly testing for Fe (such a test must measure chelated iron) and NO₃ (such a test must be accurate in the range of 5 mg/l). However, this is a troublesome, quite expensive and depending on the test used, an inaccurate method.

It may take some time to determine the correct and best fertilizer dosage for our plants, but it's worth the effort to later enjoy their healthy and beautiful appearance.

Such dosing allows the following nutrient concentrations to be maintained in the aquarium:

• NO₃ – 3-5 mg/l
• PO₄ ≤ 0,1 mg/l
• Fe – 0,1 mg/l
• CO₂ – 15-20 mg/l

Additional information and tips

With this method, there are no stringent guidelines regarding partial water changes - other users of the method suggest making a 30-50% partial water change once a week or two.

As for additional CO₂ fertilizing, its level in the aquarium should be stable, but not more than 20 ppm (20 mg/l).

Fertilizer in the PMDD method can be prepared on your own or bought ready-made. Before use, shake well and store in a dry, dark place at room temperature.

The PMDD method provides plants with a complete set of nutrients in relatively small amounts, ensures their moderate growth, and the limitation of phosphates means that we do not need such a large amount of carbon dioxide in the aquarium.

EI Fertilizing – Estimative Index

Introduction

This method was created by Tom Barr and involves dosing nutrients (also phosphates) without the need to monitor these components in the aquarium (no need for tests). In this case, the fertilizer is dosed with a slight excess to ensure that the plants will not lack any component. This excess is removed at the beginning of each dosing cycle by conducting systematic, but large water changes to prevent possible overdose of the fertilizer (inhibition of its individual components).

The EI method allows to fertilize plants in an "approximate" amount, almost exactly required by them (estimating the amount of nutrients, not dosing a strictly defined dose).

This method is particularly recommended for aquariums with strong lighting and a large number of plants, but after appropriate dose reduction can also be used in tanks with weaker light.

Composition of EI liquid fertilizer:

fertilizer with macroelements:

Compound Name	Dosage
potassium nitrate	33 [g]
monopotassium phosphate	7,2 [g]
magnesium sulfate	(*)
TNC GH Boost or Seachem Equilibrium	(**)
warm distilled or RO water	250 [ml]

(*) - add if your tap water is poor in magnesium – Mg < 5-10 mg/l;

(**) - add, if the total hardness of our water is very low, GH < 3.

fertilizer with microelements:

Compound Name	Dosage
chelate mix: 7% Fe; 1,3% B; 2% Mn; 0,06% Mo; 0,4% Zn; 0,1% Cu; EDTA; DTPA (ready-made preparations: TNC Trace, Plantex CSM+B, Microplex Chelating Agent-EDTA by Miller)	10 [g]
ascorbic acid (E300)	0,25 [g]
potassium sorbate (E202)	0,1 [g]
warm distilled or RO water	250 [ml]

EI Fertilizer Dosing

We can prepare fertilizer under the EI method ourselves or buy it ready-made. When it comes to ready-made fertilizers, we have two forms to choose from:

• fluid (e.g.: Seachem Flourish, TNC Lite, Tropica Plant Nutrition, Easy-Life Profito);
• powder (e.g.: Plantex company).

Fertilizer dosing cycle depends on:

• the number of plants (how much tank bottom surface they take up),
• the type of plants (how they absorb nutrients - through roots or leaves),
• lighting intensity;
• form of fertilizer (liquid or powder).

Liquid Fertilizer Dosing Cycle:

Day of the week	Activity
Monday	50-70% water change 5 ml per 50 l of macronutrient fertilizer solution
Tuesday	2,5 ml per 50 l of micronutrient fertilizer solution
Wednesday	5 ml per 50 l of macronutrient fertilizer solution
Thursday	2,5 ml per 50 l of micronutrient fertilizer solution
Friday	5 ml per 50 l of macronutrient fertilizer solution
Saturday	2,5 ml per 50 l of micronutrient fertilizer solution
Sunday	a day of rest

Powder Fertilizer Dosing Cycle:

Powder dosing depends on the aquarium volume and follows the same cycle as liquid fertilizer dosing.

The EI method requires daily fertilizer dosing, following a dosing cycle, so that the level of all nutrients remains stable to prevent exhaustion of any component.

The fertilizer should always be dosed at the same time of day, preferably just before switching on the light.

Fertilizer doses may be adjusted according to the needs of our plants. It is recommended to start dosing with a maximum dose and decrease it after completing a full three dosing cycles. We always make changes in the amount of fertilizer after a full three cycles. We continue to decrease the dose until we see undesired effects of too little fertilizer (poor plant condition) - then we increase the dose to the lowest level under which the plants were growing healthily (maintaining a three-week cycle).

The use of the EI method allows for maintaining the following nutrient concentrations in the aquarium:

• NO₃ – 20-30 mg/l
• PO₄ – 1-3 mg/l
• Fe – 0,5 mg/l
• CO₂ – 30 mg/l
• K – 20-30 mg/l
• Mg – 10 mg/l

Other Information and Tips

When using this method, regular (weekly) and large (50-70%) partial water changes are required. This treatment is intended to remove any excess fertilizer and organic waste from the water.

When using this method, a high concentration of CO₂ in the water is required and it must be kept at a constant level of 30 ppm (30 mg/l). The appearance of algae in the aquarium indicates that there is an inappropriate (too low) concentration of carbon dioxide in the water.

The use of the EI fertilization method also requires good water circulation in the aquarium - at least 10 times the nominal filter flow to the tank volume.

Comparison of PMDD and EI fertilizing methods

Fertilization with individual macroelements and microelements - tips

Macro elements:

1. Nitrogen N – plants respond very quickly to the addition of this fertilizer. Nitrogen in fertilizer can come in different forms that determine its dosing:
   • nitrogen in the form of ammonia – this is less efficient fertilizer, which we dose proportionally to the plant mass in the aquarium; recommended for experienced aquarists.
   • nitrogen in the form of inorganic compounds (e.g. potassium nitrate) – more effective type of fertilizer, which does not pose a threat to living organisms.
2. Phosphorus P – the amount of phosphorus is closely related to the amount of organic matter and biomass in the aquarium. Dosage of phosphorus in an aquarium, where we have a significant predominance of fish and other aquatic animals over plants, is not required. It is different when these proportions are reversed. A commonly reproduced myth is blaming phosphates in the tank for the problem with algae in the aquarium. Nothing could be more wrong - it has been scientifically proven that higher plants absorb phosphorus first. Fertilizers supplementing this element also occur in different forms:
   • phosphorus in the form of inorganic compounds, which is well absorbed by plants (e.g. potassium dihydrogen phosphate);
   • phosphorus in the form of calcium phosphate – compound poorly soluble in water, and thus ineffective.
3. Potassium K – the most recommended form of this fertilizer is liquid – so that plants can absorb potassium through the leaves. It should be dosed in the same quantity as nitrogen – its surplus is not harmful to plants, as plants store these surpluses in their cells.
4. Calcium Ca – dosage of this fertilizer requires special attention in very soft waters. Usually the concentration of this element in tap water is at an appropriate level and does not require additional fertilization.
5. Sulfur S – usually the concentration of this element in tap water is at an appropriate level and does not require additional fertilization.
6. Magnesium Mg – tap water contains much more magnesium than plants need. Therefore, the best "fertilizer" for this element will be systematic water changes. The ratio between the content of Ca and Mg in aquarium water should be 3 to 1 or 4 to 1.

Microelements:

1. Iron Fe – the effectiveness of a given fertilizer is influenced by the form of iron used in its production. Iron in the form of oxides or hydroxide does not dissolve in water, and thus is not absorbed by plants. The soluble form is chelated iron compounds – chemically stabilized by using suitable chelators (e.g. citric acid, EDTA, DTPA, HEDTA).
2. Manganese Mn – deficiencies of this element most often occur at a high pH of water. In low pH, the element is better absorbed by plants.
3. Copper Cu – dosage of this element should be very careful, as copper is extremely toxic to all organisms living in our aquarium, and also its too high concentration can inhibit the absorption of other microelements.
4. Zinc Zn - plants' absorption of zinc is closely related to the temperature of the water in the aquarium - with a decrease in temperature, the absorption of this element also decreases. This means that cold-water tanks (e.g. European biotope) may struggle with a zinc deficiency.
5. Boron B - here, the absorption of this element is influenced by the pH of the water - the higher the pH, the lower the absorption of boron. This means that aquariums with a pH >7.5 may struggle with boron deficiencies. A decreased level of B further limits the absorption of other nutrients: iron, magnesium, cobalt, potassium, and phosphorus. The dosage of this element depends on the type of plant - in what way it absorbs nutrients from the water.
6. Molybdenum Mo - deficiencies of this element most often appear in aquariums with acidic water (with a decrease in pH, the absorption of this element also decreases). Fertilizer dosage with Mo depends on the specific species of the plant.
7. Chlorine Cl - in the case of chlorine, tap water is a sufficient source of this element.

Antagonisms between individual elements:

• too high concentration of Fe – decrease in the absorption of Mn and Zn;
• too high concentration of Zn – decrease in the absorption of Cu and Fe;
• too high concentration of Mn – decrease in the absorption of Fe and Zn;
• too high concentration of Cu – decrease in the absorption of Fe, Mn, and Zn;
• high water pH – decrease in the absorption of P, Fe, Cu, Zn, Mg, and B;
• low water pH – decrease in the absorption of K, Ca, S.

Required concentrations of nutrients in a plant aquarium:

• CO₂ – 20-30 mg/l
• NO₃ – 5-30 mg/l
• PO₄ – 0.1-1.5 mg/l
• K – 5-30 mg/l
• Fe – 0.1-0.5 mg/l
• Mg – 5-10 mg/l
• Ca – 20-30 mg/l

Carbon Dioxide Fertilizing Techniques

Depending on the size of our aquarium, the type of lighting used in it, the quantity and type of plants as well as the number of fish and other aquatic animals, we can choose from one of three methods for fertilizing the water with carbon dioxide. These include:

• the use of special liquid preparations;
• the use of a homemade brew;
• the use of a high-pressure cylinder.

Liquid Carbon

The truth is that the advertised liquid CO₂ preparations have nothing to do with gaseous carbon dioxide. These preparations are ordinary fertilizers enriching our water with organic carbon. They are not an alternative to carbon dioxide fertilization, but they support its use.

By itself, this type of fertilizer works well in small aquariums (up to 50 l), especially in shrimp tanks and tanks with a small amount of light (up to 0.6 W/l). They are also often used by aquarists who use high-pressure cylinders - as an additional source of carbon.

Advantages of using liquid preparations:

• affordable price;
• efficiency of preparations;
• ease and precision of dosing;
• additional algaecidal action;
• preparations usually contain additional beneficial ingredients e.g., converting Fe 3+ to digestible Fe 2+, humic acids etc.

Disadvantages of using liquid preparations:

• overdosing preparations can kill beneficial nitrifying bacteria in the filter and substrate;
• preparations based on glutaraldehyde are unsuitable for aquariums with a pH > 7.5;
• controversial effectiveness of using only the preparations (without additional fertilizers) in doses recommended by manufacturers - opinions are divided from people who did not notice any changes after using the fertilizer, to supporters of this method.

Homebrew method

The homemade carbon dioxide fertilization system is called a homemade brew. The use of a homemade brew is recommended for medium-sized aquariums (up to 100 L) and lighting above 0.6 W/l.

The construction of a home brew is very simple - it consists of two plastic bottles connected with hoses. The operation of such a homebrew illustrates the diagram below:

To prepare a homebrew, we will need two PET bottles with caps - 2 L (for the fermenting mash) and 0.5 L (for gas filtering/cleaning). We make a hole for the tube in the cap of the large bottle. We introduce the hose through it in such a way that it enters the bottle by about a centimeter (it cannot touch the mash). In the cap of the small bottle, we make two holes and place two tubes in them - one is the one that comes out of the large bottle and the other is the one that goes to the diffuser. The tube coming from the large bottle and entering the small one must be immersed in the water as low as possible. However, the tube going to the diffuser should be as high as possible, not touching the water. We seal the tubes in the caps with silicone so that carbon dioxide does not escape through leaks (silicone dries for about 24-48 h).

To prepare the mash we use 10 dag of culinary yeast, 400 g of sugar, and 1 L of lukewarm water. We dissolve the crushed yeast in the water. We do the same with the sugar - we put both ingredients in the 2 L bottle and pour the remaining water. Such a constructed homebrew will start supplying carbon dioxide in a short time (from 30 minutes to a few hours). You can increase or decrease the amount of yeast, which will give us longer operation with a lower intensity of CO₂ or shorter operation with a stronger release of CO₂. The operation time of the homebrew varies from 1 to 4 weeks.

You can use a very fine structure air stone as a diffuser - e.g. a linden wood cube.

At night, we should stop fertilizing with carbon dioxide, because in the darkness, photosynthesis processes do not occur - plants breathe with the oxygen produced during the day, and they excrete carbon dioxide into the water. It is easy then to exceed its concentration, and consequently to lower the pH (more carbonic acid in the water - more acidification of the water), and each change in pH by 1 degree actually results in a tenfold change in ion concentrations (logarithmic function).

Advantages of using homemade brew:

• low operating costs;
• easy installation;
• good for beginner aquarists who are not yet sure how long they will be interested in this hobby.

Disadvantages of using a homemade brew:

• The life span of a moonshine distillery depends on the ambient temperature;
• no possibility of regulating the carbon dioxide emitted - gas production is continuous, which significantly affects the pH value in the aquarium;
• no option to stop gas supply at night (when the lighting is off) - large pH fluctuations in the aquarium;
• Decrease in efficiency of carbon dioxide emission over time (most is produced in the initial operating period);
• possibility of leakage of fermentation mash into the aquarium when using only one bottle or two with mash;
• in case of loss of patency (blockage of CO₂ outflow from the device) the fermentation tank may explode.

High pressure cylinder for CO2 fertilization

This method of enriching water with carbon dioxide is recommended for aquariums above 100 litres, which are strongly lit and have a preponderance of plants over animals or have demanding plant species.

A basic set for CO₂ fertilization using a high-pressure cylinder consists of:

• High pressure cylinder;
• Reducer;
• Pneumatic tube / pressure hose;
• Diffuser.

Additional components to improve the kit's effectiveness are:

• A precision valve (needle);
• A solenoid valve;
• A non-return valve;
• A bubble counter;
• A timer - on / off switch.

The set can be assembled using quick couplings (more convenient to use, but often cause leaks) or hard fittings (e.g.: nipples, sockets, etc.). The second method requires additional teflon tape or gasket sealant.

Additional accessories (gadgets) for the CO₂ fertilization set

• Carbon dioxide indicator: allows constant monitoring of CO₂ content in the aquarium;
• pH computers - allow adjusting the CO₂ dose based on the pH value of the water in the aquarium.

High pressure cylinder

Usually, cylinders used in aquaristics have a capacity of 0.5 kg or 2 kg. When choosing a bottle we should be guided by its current certifications (legalization), we should make sure that it is not regenerated e.g.: from an old extinguisher and whether it is equipped with a safety valve. An important parameter is also the possibility of refilling.

Reducer

Reducers are used to adapt the high pressure from the cylinder (reduce it) to a lower pressure used in aquaristics.

The reducers used in the CO₂ fertilization kit can have 1 clock/pressure gauge (indicates the high pressure in the cylinder) or 2 clocks/pressure gauges (one indicates the high pressure in the bottle, the other the low pressure after reduction), may already be equipped with a precision needle valve, a non-return valve and/or a bubble counter - everything depends on the manufacturer and the purpose of the reducer (those intended for aquarium use generally have all the above-mentioned elements).

Pneumatic tube

A pneumatic tube is nothing more than a plastic hose used to connect all elements of our kit. It is important that it withstands high pressure.

Diffuser

The role of the diffuser is to facilitate the dissolution of carbon dioxide in water - breaking its bubbles into the smallest possible size (so-called microbubbles).

We distinguish between internal diffusers (placed inside the aquarium) and external (placed outside the aquarium - more effective).

Internal diffusers are open on one side, can be of various shapes (pipe-like, cylindrical, "flower"), made of plastic or glass, usually contain a ceramic sinter that breaks the gas bubbles, can be integrated additionally with a bubble counter (submerged spiral) or/and a non-return valve. The internal diffuser should be placed as close to the bottom as possible, under the outflow from the filter.

External (flow-through) diffusers are completely enclosed and also contain a ceramic sinter to break the bubbles. What distinguishes them from traditional diffusers is the possibility of direct connection to the outlet hose from an external filter or circulation pump. In this way, the water flowing through the diffuser saturates even 100% with carbon dioxide. Diffusers of this type are recommended primarily for very large aquariums.

Precision needle valve

It is used for precise carbon dioxide flow regulation.

It may be integrated with one of the set elements (e.g. reducer, diffuser) or you can purchase it separately and install it in an appropriate place on the pneumatic line.

Solenoid valve

It allows controlling the carbon dioxide fertilization - it allows adapting the method to the need of CO₂ fertilization during the day and stopping fertilization at night. It is necessary to connect the solenoid valve to a timer (on/off switch) - the valve opens when connected to the power source (the valve is normally closed).

Depending on the construction of the solenoid it will heat up significantly (quite a big problem) or not. Solenoids that do not heat up during operation are impulse solenoids. Solenoids can be integrated with a non-return valve.

Non-return valve / return valve

This valve prevents backflow of water from the aquarium and protects our set from damage.

It may be integrated with one of the elements of our set (e.g. solenoid) or you can buy it separately and mount it in an appropriate place on the pneumatic tube.

Bubble counter

It allows controlling the carbon dioxide flow - with its help we can count bubbles in a unit of time.

It is usually a glass or plastic cylinder topped on both ends with suitable outlets for connection to the pneumatic tube.

How to assemble the CO2 fertilization kit

The following diagram illustrates how to connect the kit:

1. Before starting to assemble the set, we should soak the diffuser membrane (ceramic sinter) in warm water for at least 24 hours prior.
2. The reducer should be tightly screwed onto the high-pressure cylinder. Proper operation of the reducer requires the cylinder and the reducer to be positioned vertically.
3. Cut the pneumatic hose to the required length. Attach one end to the pre-soaked diffuser, the other end to the reducer. To make the hose more flexible, you can soak the ends in warm water beforehand.
4. Attach additional elements in the correct order, cutting the pneumatic hose each time - precision valve after reducer, then solenoid valve, check valve, and bubble counter.
5. Install the bubble counter as close to the diffuser as possible and fill it with water. To facilitate this process, cut the hose at the appropriate place; detach the hose part from the solenoid valve; attach the counter outlet to one end of this part; submerge the counter in the aquarium, fill it completely with water; to stop the water, leave the counter submerged and reconnect the other end of the previously detached hose part to the solenoid valve; remove the counter from the aquarium and connect it to the pneumatic hose (the part from the side of the diffuser). Attach the bubble counter to the outer wall of the aquarium.
6. We can start the connected set. Before opening the main cylinder valve, make sure all reducer valves are closed. Then, open the main cylinder valve completely and then reverse it by half a turn (the reverse valve is to prevent possible jamming in the future). With the cylinder completely filled, the pressure gauge should indicate a pressure of approx. 60 atmospheres. During use, this pressure will gradually decrease to zero.
7. The proper gas flow adjustment is done using the precision (needle) valve - we observe the flow of carbon dioxide from the diffuser or adjust it to the appropriate number of bubbles per unit of time on the bubble counter (if we have one).
8. Keep in mind that the more connections in our set, the more likely a leak will occur and the faster the gas consumption. You can check the tightness of connections by lubricating them with water mixed with foaming agent (e.g., dishwashing liquid) - the appearance of bubbling blisters will confirm breaks in the system. Leaks usually occur at the cylinder-to-reducer connection (the thread is best secured with Teflon tape or pakul tape) and quick couplings (especially when the set is assembled and disassembled frequently - the pneumatic hose wears out, it expands).

How to control the amount of carbon dioxide in the aquarium.

As you know, an improper level of carbon dioxide carries serious consequences - too much of it rapidly lowers the pH of the water and causes diseases in fish (a disease caused by lack of oxygen). An overdose of CO₂ is also bad for the condition of plants, as its presence in water affects the speed at which they absorb other nutrients. The more CO₂, the faster and easier we can lead to macro and/or micro element deficiencies, and therefore their deficiency and poor plant condition. In this situation, algae outcompete plants for nutrients and quickly begin to dominate the aquarium.

That's why proper dosing of CO₂ seems so important. Carbon dioxide in water is measured indirectly, based on the measurement of its pH. For this purpose we can use:

• pH stripes - they are inaccurate;
• CO₂ indicators - the result is read with a delay;
• pH meters and pH computers - expensive, require additional reagents (buffers) and precise calibration;
• gradually increasing CO₂ and observing life in the aquarium - a time-consuming method but recommended by most aquarists - it involves initially setting the gas flow value to 1 bubble/second; after an hour of observing life in the aquarium, we increase the dose by another bubble (2 bubbles/second) and again observe the behavior of fish and the condition of plants; we increase the carbon dioxide dose until we notice signs of fish suffocating (fish moving violently, decreased or no appetite, intense opening of the gill covers, staying close to the water surface, pecking, etc.); then we reduce the carbon dioxide dose to the previous one, in which these symptoms did not occur.

Tips for fertilizing plants with carbon dioxide

Carbon dioxide is present in water at a concentration similar to that in air, but in water, this gas dissolves about 10,000 times slower than in air. Its concentration is closely related to carbonate hardness and water pH. The higher the carbonate hardness, the smaller the pH and carbon dioxide fluctuations. The higher the water pH, the lower the CO₂ concentration. Without additional CO₂ fertilization, plants grow 6-10 times slower than when the gas is fertilized.

Additional carbon dioxide fertilization is not necessary in poorly lit aquariums with less demanding plants. But then we have to provide a few hours break in lighting for the CO₂ absorbed by plants to regenerate (plants do not absorb carbon dioxide from water without light - on the contrary, they excrete it).

Additional carbon dioxide fertilization is necessary in strongly lit aquariums when we have a predominance of plants over aquatic animals. We also dose this gas when we grow submerged mud or terrestrial plants that grow completely emerged in their natural environment.

When we have the lighting turned off and it is dark, we never fertilize water with carbon dioxide - plants without light do not absorb CO₂.

The amount of light and carbon dioxide is interrelated and it affects the speed at which plants absorb other nutrients. The less carbon dioxide in the aquarium, the less light we need.

With carbon dioxide fertilization, very good water circulation in the aquarium is recommended, but it is not recommended to use undergravel filters or air pumps - they accelerate the evaporation of gas from the tank.