CO2 system for aquariums

Carbon dioxide injection system to stimulate the growth of aquatic plants. Transform a mediocre planted aquarium into an underwater garden.

Detailed explanation

Aquatic plants use CO2 as a carbon source for photosynthesis. In the air the CO2 is at 0.04%, in the water the concentration is even lower. Without supplementation, plants grow slowly and struggle to compete with algae.

A pressurized CO2 system is composed of: cylinder (refillable or disposable), pressure reducer with pressure gauge, solenoid valve (to turn off the CO2 at night), bubble counter and diffuser (ceramic or inline atomizer).

The target concentration is 20-30 mg/l of dissolved CO2. It is adjusted by monitoring the drop checker, a solution indicator that changes colour: blue = too little CO2, green = just right, yellow = too much.

CO2 should only be injected during daylight hours when plants photosynthesize. At night, plants breathe by consuming oxygen and adding CO2 in the dark risks suffocating fish. The solenoid valve connected to a timer solves the problem.

Yeast systems (do it yourself with sugar and brewer's yeast) are an economical alternative for nano aquariums but the production is not constant and cannot be regulated.

CO2 tablets and carbon-based liquid fertilisers (such as Seachem Excel or Easy Carbo) are less effective alternatives to injection but better than nothing for undemanding plants.

The pH drops when CO2 is injected because the dissolved CO2 forms carbonic acid. This must be taken into consideration: in water with low KH the injection of CO2 can cause the pH to drop dangerously.

An inline diffuser (mounted on the external filter tubing) produces very fine bubbles with the best dissolution. Ceramic atomizers in aquariums work well but produce a mist of bubbles that some find unaesthetic.

Reference values by aquarium type

How it is measured

Drop checker with 4 dKH solution and pH indicator. Green = 20-30 mg/l. Yellow = too much. Blue = little. Alternatively it is calculated from pH and KH using specific tables.

What happens when it is too low

Plants that grow slowly. Pale leaves. Algae taking over. Demanding plants (ground cover, red) suffer visibly.

What happens when it is too high

Fish gasping at the surface. pH dropping below 6.0. Shrimp trying to get out of the water. In extreme cases, fish die from asphyxiation.

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