[oakleyhoma]

First, thanks for your comments. AquaristFist: did you mean a powerhead/sponge combo is fine, no problem with oxygenation (provided I use a HOB too?). confuted: sorry I was confusing - I don't know if there is anything wrong with the powerhead/sponge combo vs. pump/stone/sponge. And it would be quieter I think. But if powerhead/sponge meant not enough oxygenation/water purity for the shrimp (even with a HOB also, for mechanical filtration) I'd consider a pump/air stone/sponge combo. I could put the pump in a small box to quiet it and the stone might not be too noisy. Or I could set the pump/sponge on a timer to run only at night, so I don't hear it and to not rob the water of CO2 during the daytime when my moss and java fern would need it.
If this makes better sense, then ... thoughts appreciated.