At the beginning, I would like to briefly explain some basics for the aeration of the GN-Jet lifter®.
The water column above the drive creates a counterpressure that the air must overcome in order to be able to exit the air hose into the aquarium at all. 1cm of water depth corresponds to approximately 1 millibar of back pressure. If the jet lift drive is located at a water depth of 30 cm, the diaphragm pump must apply more than 30 mbar in order to blow air into the drive at all.
The air volume indicated on the air pumps in litres/minute or per hour is only valid at the indicated water depth. As the water depth increases, the air volume decreases considerably. Good air pump manufacturers supply a characteristic curve showing this relationship.
Long 4/6mm air tubes act as a resistance. At the end of a long, thin tube, considerably less air arrives than comes out of the pump without an air tube. If several tanks are to be supplied, the air should be routed to the tanks with as thick a hose as possible, and the 4/6mm tube should be as short as possible. A ring supply of PVC pipes above the pools is the optimum, but is not always feasible for optical reasons.