Dave, Additional elevation should not affect the pumping. However note that each diffuser will need a valve (ball valve) on a separate air line to regulate the air flow. Otherwise all the air will want to go only to the shallowest diffuser. I prefer to split the air at the pump with a manifold and valves. However some get it done by splitting the air at the water's edge. This exposes the valves to the elements and often causes extra problems.
