JBL CO2 Direct Test


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JBL Aquatics


JBL CO2 Direct Test

Quick CO2 test kit to determine the carbon dioxide content (main nutrient for plants) in freshwater aquariums. Simple and easy to use.

  • Simple and reliable monitoring of the aquarium water values. Determines the optimal carbon dioxide content for freshwater aquariums
  • Procedure: fill plastic cuvette with sample water, add reagent drop by drop until pink colour remains stable. Number of drops x 2 = CO2 content in mg/l
  • To use during periods of poor or no plant growth and fish mortality: once a week
  • You will find detailed information and troubleshooting tips about water analysis on the JBL website in Essentials/Aquarium
  • Package contents: 1 CO2 test kit incl. 2 reagents, plastic cuvette and colour chart. Reagent refill separately available

Instructions CO2 Test

Features: JBL PRO AQUATEST Ca is an easy-to-use titration test to determine the carbon dioxide content of freshwater.
Why test? Carbon dioxide (CO2) is the most important plant nutrient. The consump-tion of CO2 differs from aquarium to aquarium and depends, amongst other things, on the following factors: number and demands of plants, carbonate hardness, water movement and light. Fertilisation with CO2 is usually done with a CO2 fertiliser system. In the aquarium water, a CO2 content between 15 and 30 mg / l is recommended. This range is safe for fish and at the same time ensures luxuriant plant growth. 20–25 mg/l CO2 has proven to be ideal. In special aquariums with a large number of plants, higher values of up to 35 mg/l may be required.

With this test you can determine the CO2 content of your aquarium water in mg/l. Thus, monitor the setting of your CO2 fertiliser system.

Please note: When fertilising with so-called liquid carbon, fertiliser monitoring with JBL PRO AQUATEST CO2 Direct is not possible because these fertilisers do not con-tain CO2 but other carbon compounds.


1. Rinse the measuring vessel and syringe several times with the water to be tested.

2. Using the syringe, insert 20 ml of bubble-free sample water into the measuring tubes.

3. Place the measuring tube on both elds of the enclosed colour chart.
4. Pour 5 drops of reagent 1 into the measuring tube on the white eld and swirl it until it is mixed.
5. Add reagent 2 drop by drop. After each drop, swirl and count the drops until a pink colour is obtained which remains stable for 60 seconds and corresponds to the colour in the second measuring tube on the pink colour eld. To compare the colours, look into the tubes from above.

6. The number of drops multiplied by 2 gives the carbon dioxide content in mg/l. Example: 10 drops of reagent 2 = 20 mg/l CO2.

Since other acids in the water impair the measurement, a blank value must also be determined. To do this, take a water sample of 100 ml and aerate it for 15 min using a JBL ProSilent air pump with an air stone. Then determine the blank value according to the instructions given above.

Result–blank value = actual carbon dioxide concentration in mg/l.


To earn more about using CO2 in the aquarium CLICK HERE.

More details on this product, including full instructions, can be found HERE.



JBL Aquatics

Additional information

Weight N/A

Test Kit, Test Refill

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