Why is a backflow protection device absolutely necessary?
As long as CO2 is fed into the aquarium through the CO2 supply hose, there is no danger of aquarium water entering the hose. However, if a solenoid valve interrupts the CO2 supply at night or the CO2 supply bottle is empty, the CO2 remaining in the hose will dissolve in the water and aquarium water will continue to migrate into the hose. If it reaches the technical parts such as the solenoid valve or pressure reducer, it can lead to corrosion (rusting) and destroy them. The backflow protection works like a valve that only lets the CO2 gas pass through under pressure in one direction (direction of the arrow on the housing).
Where should it be mounted?
Ideally as close as possible to the aquarium water, just above the water level. This way, very little CO2 can migrate into the tube.
This backflow protection is not suitable for air supply systems (diaphragm pumps/air pumps), as the air pumps do not build up the correct air pressure as CO2 systems with CO2 gas can. There is a separate backflow stop for air pumps: JBL ProSilent Safe.