This Fish Tank Bubble Stone Aerator s a must-have for your aquarium! It comes with one bubble stone that you can connect to an air pump! This stone increases the oxygen levels and decreases the CO2 levels in your fish tank. It also generally improves the PH level in the tank which is good for your pets. It has a nozzle that is suitable for 4-mm tubes. By connecting it, it will then produce bubbles that will maintain the oxygen levels in your tank.