Drop checkers are used to monitor the CO2 levels in the aquarium: the pH indicator solution inside the bulb section will change color according to the amount of CO2 dissolved in the aquarium water. Blue and dark-green colors will indicate low CO2 levels, light-green (lime-green) is OK, yellow is too much. Note that drop checkers always have a delay of 2-3 hours, so they show a CO2 level that was present hours before the reading (delayed reading).

The drop checker is the best tool to monitor CO2 levels continuously. With some practice and experience it can be a precise tool to measure the amount of CO2 dissolved.

IMPORTANT: You will also need a Drop Checker Reagent (sold separately) to use this item.