Check Solution for CO₂ Long-term Tests

The DRAK CO₂ long-term test solutions for 20 resp. 30 mg/l CO₂ can be used in any conventional CO₂ long-term test for the long-term measurement of the optimal CO₂ concentration. The continuous control of this most important plant nutrient is elementary for the well-being and growth of your aquatic plants. The control of the CO₂ concentration via an endurance test with our CO₂ endurance test solutions works completely independently of the aquarium water. It therefore has the advantage that no substances such as humic acids or phosphates can interfere with or influence the measurement.


  • Depending on the system, fill 1 to 3 ml of the CO₂ long-term test solution into the long-term test
  • Place the permanent test in a place with sufficient water movement  in a way that it is well readable
  • After 1 to 2 hours the equilibrium with the aquarium water is reached
  • The green colour indicates the optimum CO₂ concentration of 20 resp. 30 mg/l - blue stands for too little, yellow for too much carbon dioxide

How it works

Nature does not like differences in concentration and compensates this by diffusion. Since diffusion takes time, the reaction of the long-term test lags somewhat behind reality. The test must therefore always be allowed the above-mentioned 1 - 2 hours reaction time after changes. Therefore, the CO₂ concentration of the test liquid of the long-term test is in equilibrium with the CO₂ concentration of the aquarium water via the air bubble between the two liquids.
The pH indicator bromothymol blue is used as the colorant of the test solution, which changes from blue (higher pH) to green and yellow (lower pH) at pH 6.6. The pH value of the test solution is influenced by the CO₂ concentration of the water in the aquarium. The carbonate hardness (buffer) of the test solution set during the preparation of the solution determines which pH is reached at which CO₂ concentration. This ensures that the solutions turn light green at the desired CO₂ concentrations of 20 or 30 mg/l, respectively.
The long-term test is therefore a useful instrument for controlling the content of carbon dioxide, which is essential for aquatic plants, with sufficient accuracy. Optimal growth is not possible without sufficient CO₂.


Please replace the solution if it fades or shows different colours (i.e. not blue, green or yellow). This is due to bacterial decomposition of the ingredients. The long-term tests should therefore be kept carefully clean. We recommend regular cleaning or disinfection every 3 - 6 months by soaking the device in diluted hydrogen peroxide or hypochlorite solution for a few hours.
A filling should work for at least 2 - 3 weeks, otherwise we would recommend disinfection as soon as possible.

The same applies to the solution in the bottles: Never touch the neck of the bottle with your bare fingers and never pour anything back into the bottle. Do not leave the bottle open longer than necessary.
Use disposable pipettes or syringes with cannulas for filling.

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Elegant CO₂ Long-Term Test in Glass including Suction Cup
Permanent and easy determination of the optimum CO2 concentration

Variants from €8.30*
Single-use cannula 0.8 × 40 mm
For filling electrodes with KCl solution using our disposable syringes

CO₂ Long-term Test (Drop Checker)
For  constant determination of the CO₂ level

Variants from €9.40*
Long-term CO₂ test Nano-Clip made of glass
Simply hang over the edge of the aquarium!

Single-use Syringes PE/PP with Luer Plug Connection
Disposable syringes PE/PP with Luer plug connection in different sizes

Variants from €0.50*
Disposable Pasteur Pipettes, graduated
For filling all standard pH tests and other tricky filling tasks


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