Drop checker + 4dKH ref

Description

A drop checker is a small glass vessel of indicator solution placed inside a planted tank to show the CO2 level in the water. The chemistry literature names it: a 2023 review of colorimetric CO2 indicators gives the drop-checker CO2 indicator used in aquaria as an example of the older indicators in which a pH indicator dye was dissolved in an aqueous solution. The same review explains how such indicators work. They use a pH indicator dye which responds to the change in pH in the surrounding medium due to the formation of carbonic acid, and in most of them enough base is present that the partial pressure of CO2 is related directly to the concentration of hydrogen ions. In an aqueous indicator, the review says, that base is usually sodium bicarbonate. The kits sell the solution ready made. NilocG's kit includes a glass drop checker, suction cup, and a 60ml bottle of 4dkh/pH reagent solution, and says it gives a reliable reading in about 2 hours. Pawfly's kit tells buyers to add 20 drops of reagent into the tubing and attach it vertically to the tank wall with a suction cup, with the note that the tubing opening must face down, and it too says results will appear in about 2 hours. NilocG says green or light green means the optimal level of carbon dioxide, that yellow means the CO2 level in the water is very high, and that blue means there is an insufficient level of CO2; Pawfly's scale reads the same way. The colour scale is the sellers' own, not a calibration.

Sources

• pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC10391618/
• amazon.com — https://www.amazon.com/dp/B01MY87WVP
• amazon.com — https://www.amazon.com/dp/B0GZP2QKHH

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