> >Don't turn off your undergravel filter, Do not. When you turn off your >undergravel, all that nice bacteria dies due to the lack of fresh oxygenated >water reaching it. This may 'crash' your whole tank. If you are using the >airstone and pump method on the undergravel, think about switching to >powerheads (which create currents but no massive bubbling). > Umm, can anyone explain what powerheads are? g