Refill cans, ideal for beginners and low light tanks, with low CO2 demands, these sets are the perfect co2 supply for small planted aquariums. The Ista Disposable CO2 Can is easily adapted for any kind of aquarium you have. If setup correctly, you could have CO2 supply for several months. For low light tanks, the rate of 1 bubble every 5 seconds usage for months. 3 pack.