To check the back pressure of one or two diffusers, hook one or both up out of the water to the pump - short hose or long hose. Read the pressure. It should be 0 if the pump is getting rid of all the air it is making. Most 9" membranes will not cause any back pressure hooked and run out of the water. Some Vertex brand diffusers will have a built in back pressure when connected & operated out of the water to the pump. Other membrane disk diffusers do not have this characteristic.
Cheapest redneck air filter is a threaded nipple out of the pump and a cloth rag wrapped several layers and secured around the nipple.
Last edited by Bill Cody; 05/24/18 08:49 PM.
