Description: This glass CO2 drip checker is used to monitor the CO2 dose in the aquarium. Simply fill the CO2 indicator solution, and the solution will change color to indicate the CO2 content in the aquarium water. The CO2 inspection glass and suction cup are included in the package. How to set up a CO2 indicator solution for a CO2 checker: Add 4 dkH reference solution to your droplet checker. In addition, you need to add 3 drops of pH indicator. (It is bromothymol blue). Features: Aquarium CO2 Monitor Carbon Dioxide Glass Drop Checker with 15ml Monitor Fluid. A different color of the liquid represents a different concentration of CO2. Blue means the CO2 concentration is too low. Green means this is normal. Yellow means the CO2 concentration is too high, excessive CO2 can cause the death of fish and shrimp from oxygen deficiency. What is 4 dkH: 4dkh water is used in the droplet checker because it has a reliable buffer level, which happens to make the color change of the indicator fall on about 30 ppm CO2. The hardness of the water in the storage tank does not matter. In theory, it will not come into contact with the contents of the droplet checker and therefore will change the color. Use liquids of different intensities to move the indicator's changing points to adapt to different CO2 levels. includes: 1x Detection solution 1x Detector