I am adding a #4 sponge filter to my 75G, which already has a canister filter. The Air pump instructions (Fusion 400) say to locate the pump 12" above the aquarium, and use a check valve.
However, other brands of pumps say to locate the pump above the tank, or lower than the tank if a check valve is used.
Is this a case of over-cautiousness, or are air pumps prone to fail and siphon off the tank contents?
What do you do?
Is it possible or necessary to use 2 check valves?