The Ista Water Plant CO2 tablets provide an easy and convenient way to provide Co2 for your aquarium plants. It works by gradually dissolving and releasing CO2 into the aquarium water. It takes about 2 hours for the Co2 tablet to dissolve completely. Use 1 tablet per 20 liters of water to add about 5mg/L CO2. Apply daily. Planted tanks should maintain a CO2 content of 5-15mg/L. 100 tablets.