dbw, are you aerating otherwise (i.e. w/ bottom diffusers)? pumping air is alot cheaper than pumping water, at least it is in CA.

if the bass was not gulping or looking otherwise stressed, he's probably o.k. and was just hanging in the shallows in the early a.m. i see this routinely in a local pond and nearby reservoirs that have no oxygen problems.

as far as yer other questions, wait for the circulation masters chime in.

GSF are people too!