ISTA CO2 Tablet Carbon dioxide 100 TAB Carbon dioxide - Planted Diffuser Tablets by Aquarium Equip Easy and convenient way to provide Co2 for your aquarium plants to thrive. By gradually dissolving in the water to release Co2 into the aquarium water.  Provide same function and effect to bottled gas Co2  Simply drop the Co2 tablet into the aquarium water. It takes about 2 hoursfor the Co2 tablet to dissolve completely. Provide same function and effect to bottled gas Co2  Simply drop the Co2 tablet into the aquarium water. It takes about 2 hoursfor the Co2 tablet to dissolve completely. Simply drop the Co2 tablet into the aquarium water. It takes about 2 hoursfor the Co2 tablet to dissolve completely.