Description ANS OPTI GLASS CO2 CHECKER GLASS ANS Drop Checker measure accurately the amount of CO2 in the water. Opti glass material used enhances elegant visual effect to your planted aquarium. As all planted aquarium are different, the amount of CO2 intake by plants are different. To measure accurately if the amount of CO2 is enough, we use CO2 monitor device. CO2 monitor device accurately measure the amount of CO2 dissolved in the water.