Thin the mesh a little. It could be too thick. Either that, or use gutter guard, not that stuff. I know that in general, bigger impeller means more flow, but not with needlewheels all the time. The centrifugal force is what the mesh is there for, with impellers, much of the water doesnt even pass through the impeller itself, it merely passes between the impeller and the shroud intake area to the outer ring of the pump housing. The same goes for needlewheels. Much of the water and bubble mixture doesnt even get mixed in the impeller, it bypasses the needlwheel all together and makes a b-line to the outlet, being pulverized by the other bubbles on the way... not the needlewheel.
What Im trying to say is that I doubt having such a thick and dense foam disk is doing much for you. The outer edge of the disk might lose some of its centrifugal force capabilities, but the thickness of the 'mat' isnt going to do much for bubbles... as its too thick for much of anything to make it to the inner depths of the mesh.
OTOH, too thick of a pad could place a restriction on the intake air and water mixture. If this space is too narrow, and the pad is as dense as it is, its going to make a restriction. Those tall needlewheels you see for the dart still alow alot of mix to pass through the needles... not so true with the dense mesh.
I would try it again with the pad thinned out.
And as for the pad behind the plate... there is no point. Being that the backside of the impeller cant draw air/water from anywhere, all it can do is cause cavitation if anything.
Thinning the pad by making its area thinner, or making its density less by using gutter guard rather than dense mesh might be a good idea. Also, hybrid designs seem to work well with pumps like this... keeping the regular impeller blades allows the pump to keep more of its throughput, but wrapping them with mesh allows them to blend better. It might be the best of both worlds here.
