i really dont go by turnover rates for filtering "healthwise". bio does a more efficient job at a lower gph, while mechanichal does better at a higher gph, excluding extremes either way. mechanichal filtration is for your benefit to keep the tank looking clean, not the fish, as the poo is still in the water, whether it be in the filter pads or floating about the tank. i always tend to overfilter, but i certainly could run my tanks off of air driven sponge filters with no gph.