CO2 - the basic food for your aquarium

The main nutrient for plants is carbon dioxide (CO2), which they transform during photosynthesis with the help of light energy and water into food (sugar), releasing oxygen as a by-product.

As a consequence the use of a CO2 fertiliser system is the most important way to supply your plants with food. Certainly there is CO2 dissolved in your aquarium water, but for most plants this is not enough for a vigorous growth.

If you know the carbonate hardness of your water you can read in the table shown, how much CO2 is present in your aquarium water. The green area in the table indicates what would be the ideal CO2 level for thriving plant growth or the right level for sensitive plants. Now you can see whether the CO2 content of your water is not sufficient and you need to increase it for the perfect plant growth. JBL offers you a practical JBL CO2-pH Permanent Test , which permanently displays the CO2 content of your aquarium water. This way you can easily and quickly read on a scale at any time how much CO2 is available in the water. The CO2 permanent tests always need a few hours before the CO2 content in the water is indicated. A quick and very precise method to determine the CO2 content offers the JBL CO2 Direct Test . Here you add an indicator liquid into a sample of the aquarium water and you count the drops until a stable pink colouration appears. With this test you also have the opportunity to exclude other acidic effects from the test results. Simply carry out the test once more with an aerated sample and then subtract the difference between the two tests. The CO2 gas is expelled during the second test and this difference is taken into account by the subtraction.

The plants’ staple food: the CO2 fertilisation

What is CO2?

Carbon dioxide (CO2) for plants corresponds to carbohydrates + fats + proteins in human nutrition, i.e. the most important "staple foods" without which we cannot survive. However, we still need vitamins and minerals as a supplement, whereas plants only need minerals. For this purpose we have the fertilisers in the JBL PROFLORA FERROPOL range. During photosynthesis, plants use light energy to bind CO2 with water and turn it into sugar (their actual food). This process releases the oxygen as a "waste product" which we humans & animals need to breathe. At night plants reabsorb a small part of the oxygen to respire.

How does the CO2 enter your aquarium water?

Can you manage without the CO2?

Admittedly, even without CO2 fertilisation, some aquarists have observed their plants growing. There are several reasons for this, and the needs of aquarium plants can differ as much as those of fish (discus/goldfish). Some plants, such as the Vallisneria, need very little fertiliser, little light and can survive with the CO2 content of untreated water. Any high maintenance plants, such as Rotala macranda, would perish miserably if forced to share an aquarium in these conditions. The Vallisneria, on the other hand, would flourish still further, were it to receive CO2 fertilisation, assuming there is enough fertiliser and light.

Left without, right with CO2 addition

CO2 is dissolved in EVERY water, as it diffuses from our air into the water. Unfortunately, it’s not enough for most aquarium plants. In the following table you can read how much CO2 is dissolved in your aquarium water at a certain pH value and a carbonate hardness X. The ideal CO2 content is marked in green. This makes it easy to see how much CO2 is still missing in your aquarium water so that your plants get enough nourishment.

The correct CO2 content in the aquarium

In the table, the optimal CO2 content is colour-coded. As you can see, each water hardness is assigned a certain CO2 value, which then determines the pH value. Although even at high hardness levels (e.g. 14 dKH) a pH value of 6.2 can be achieved by adding CO2, the amount of CO2 (265 mg/l) required to achieve this is fatal for the animals in the aquarium. If an aquarist wants to achieve a low pH value of - let’s say - 6.2, it’s better to first lower the carbonate hardness to 2 (e.g. by adding osmosis water). Conversely, the table also shows if there is too little CO2. If an aquarium has a KH of 6 and a pH value of 7.4, the natural CO2 content is only 7 mg/l. By adding CO2, a CO2 content of 15 - 30 mg/l should be aimed for, which in turn will lower the pH value to 7.1 - 6.9.

Why is CO2 so good at combating algae?

Plants and algae are food competitors in the aquarium. If the plants grow well, there is hardly any food left for the algae and they wither away. CO2 fertilisation promotes the growth of the plants so that the algae don’t stand a chance! Even in aquariums where only a few plants live (as is often the case in Malawi-Tanganyika aquariums) these few plants need to be nurtured all the more intensively in order to actively combat algae growth. Incidentally, compared to the supply of nutrients, light plays a very subordinate role in algae control!

Does CO2 fertilisation mean less oxygen in the water?

A lot of people believe that CO2 reduces the oxygen content in the water. This is not correct! Nevertheless, let’s explain the connection in more detail. If, despite adding CO2, you move the water surface a lot with bubbling stones or spray bars from the filter, the oxygen content in the water is increased, but at the same time the CO2 is expelled again (it’s like shaking a cola bottle). The calmer the water surface, the more CO2 remains in the water. Both gases (CO2 and O2) can be present in the water in high concentrations, e.g. if the plants assimilate strongly during the day (then a lot of O2 is produced) and at the same time a lot of CO2 is added via a CO2 fertiliser system.

Aeration AND CO2 addition at the same time is absolutely pointless.

How does a CO2 fertilisation system work?

With the help of a CO2 fertiliser system you can increase the CO2 content in your aquarium water and lower the pH value. You can choose between a "Bio-CO2" system (CO2 production via a biological fermentation process) and a CO2 fertiliser system with a pressurised gas cylinder (disposable or reusable), containing CO2. The transparent CO2 gas is fed through a hose into a bubble counter in which CO2 bubbles can be counted and then dissolved in the aquarium water using a reactor/diffuser. The next stage of expansion is the addition of a solenoid valve that shuts off the CO2 supply at night, as plants do not need CO2 then. The most professional is the third expansion stage, in which the CO2 supply is regulated by a small CO2/pH control unit. It measures the pH value of your aquarium water via a pH electrode and then regulates the CO2 supply automatically.

First steps in CO2 plant fertilisation:

For aquariums between 10 and 110 litres, a biological CO2 system is a good choice. Here the CO2 gas is produced through a biological fermentation process lasting about 40 days. When the CO2 production stops, simply add new microorganisms and the process starts again. If you would like to try out how well CO2 addition works on your aquarium plants, you can start inexpensively with the JBL PROFLORA CO2 STARTER BIO SET in aquariums between 10 and 40 litres. For aquariums between 40 and 80 litres we have developed the JBL PROFLORA CO2 BASIC BIO SET, which contains a more effective gas diffuser and a professional reaction canister as well as a backflow protection. The JBL PROFLORA CO2 ADVANCED BIO SET is available for aquariums from 40 to 110 litres. In addition to the components of the "STARTER" version, this also contains a thermo casing for still more powerful and uniform bio-CO2 production. Furthermore, the bio-reaction components are included 2x, so that it runs for 2x 40 days before it has to be restarted with refills.

CO2 fertilisation with CO2 pressurised gas storage cylinders

There are different versions available for aquariums from 40 to 600 litres. In principle, there is always a low-cost starter set (BASIC), an extended version with a night cut-off (ADVANCED) and an expansion stage with fully automatic CO2/pH control (PROFESSIONAL).

Starting with CO2 fertilisation (with CO2 pressurised gas storage cylinders)

The sets of the "BASIC" range contain all components to visibly promote the growth of aquarium plants by adding CO2. You have the choice between a set without a CO2 supply cylinder (VARIO system), if a cylinder is already available, with a disposable CO2 storage cylinder (U system) or a refillable CO2 storage cylinder (M system).

Apart from the CO2 storage cylinder, all the components are identical in all three systems: A pressure reducer lowers the pressure of the storage cylinder so that you can adjust it easily and precisely with a handwheel. A CO2-resistant hose leads the CO2 gas to a bubble counter in the aquarium, where you can precisely adjust the amount of CO2 supplied by means of rising CO2 bubbles. This bubble counter contains a built-in check valve that prevents aquarium water from flowing back into the technical components. From the bubble counter, the CO2 reaches your aquarium via a hose, where it is fed into the aquarium water as very fine bubbles via an attractive glass diffuser. This way, your aquarium plants can absorb their main nutrient, carbon dioxide, from the water.

The JBL PROFLORA CO2 ADVANCED SET U contains all components including a 500 g disposable cylinder.

The JBL PROFLORA CO2 ADVANCED SET M contains all components including a refillable 500 g reusable cylinder.

The advanced CO2 fertilisation for smart aquarists:

Since plants do not need/consume CO2 at night, adding CO2 at night is unnecessary. The JBL PROFLORA CO2 ADVANCED SETs therefore contain a solenoid valve which switches the CO2 supply on and off using a timer (timer not included). You can use the timer you use for your aquarium lighting. In this way, the CO2 is switched on in the morning along with the light and switched off again in the evening. This saves almost half the CO2 and the additional costs for the solenoid valve are recouped in no time. This ADVANCED SET is available with a disposable (U system) or refillable (M system) cylinder. If you already have a CO2 storage cylinder, you can choose the JBL PROFLORA CO2 ADVANCED V(ARIO) SET, which contains all the other components, including the solenoid valve, apart from the cylinder.

For aquarists interested in water chemistry: During the course of the day, CO2 consumption leads the pH value in the aquarium to increase and this indirectly means a decrease in carbonic acid. A decrease in acidity in the water leads to an increase in pH. At night, the process is reversed: No more CO2 is consumed, but some CO2 is still produced by the plants in the dark phase. Thus the pH value decreases overnight. If the CO2 supply is NOT stopped at night, the pH value would drop even more overnight. A night switch-off, whether by turning off the cylinder or using a solenoid valve, is therefore definitely advisable. (Exceptions are the bio-CO2 systems, as they never produce enough CO2 to influence the pH value very much).

Fully automatic is also an option:

If you’re looking for sophistication, try the PROFESSIONAL version. Here, the solenoid valve is not switched using a timer, but by using a CO2/pH control unit. Simply enter the carbonate hardness you measured in your aquarium water (determined with JBL PROAQUATEST KH) into the CO2/pH control device and let it calculate the correct amount of CO2 for your aquarium, based on a pH measurement via a pH electrode. (The pH electrode needs to be purchased separately, as it should always be factory-fresh, as opposed to ageing in the set). This way, the CO2 plant fertilisation is fully automated and the pH value in your aquarium is always kept at the ideal level. Here you can choose whether the set contains a disposable CO2 cylinder (U system), a refillable CO2 cylinder (M system) or no CO2 cylinder at all, in case you already have a CO2 cylinder (V system).

For aquarists interested in water chemistry: A small part of the added carbon dioxide reacts with the water to form carbonic acid. Since any addition of acid lowers the pH value, the addition of CO2 also lowers the pH value. The pH electrode measures the current pH value of the aquarium water and the CO2/pH control unit compares it with the ideal pH value which the unit has calculated. To calculate the ideal pH value, the existing carbonate hardness needs to be measured (JBL PROAQUATEST KH) and entered. It is then taken as the basic value. The harder the water, the more CO2 is needed to lower the pH value significantly. But then there would be more than 30-40 mg/l CO2 in the water, which in turn would be dangerous for the animals. (These correlations are taken into account by the CO2/pH control unit).

To increase the CO2 concentration there are fertiliser systems ( PROFLORA CO2 plant care ). You have the choice between bio-CO2 systems, which produce CO2 by means of a sugar-yeast system and systems with pressurised gas cylinders, filled with CO2.

You can find more about the JBL ProFlora CO2 systems here: CO2 plant fertilisation .

JBL PROFLORA CO2 Premium Service Partner

In the dealer search below, you can find out which specialist dealer in your area carries the JBL PROFLORA CO2 concept and can help you fill or exchange the JBL PROFLORA CO2 cylinders by entering your postal code.

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