Tropica CO2 diffuser 3 in 1 contains a bubble counter, reflux valve and diffuser in just one unit. The bubble counter enables easy and accurate CO2 dosage, since it is easy to count the big bubbles inside the chamber during adjustment. A reflux valve prevents the aquarium water from being sucked backwards, which is possible when the bottle gets empty, or in case you use a magnet valve to turn off the CO2 supply during the night.Tropica CO2 Diffuser 3 in 1+ bubble counter, non-return valve and ceramic diffuser in one unit+ customised ceramic disc, ensuring the efficient creation of micro bubbles+ increases the CO2 utilisation as opposed to a regular air stone+ ceramic disc availale separately for replacement