so what i am thinking is would it be better to have the sump flow somewhat in reverse? what i mean is to have the water flow up thru the scrubbies instead of down onto them? i am thinking dwell time and saturation would be better.
Turnover (dwell in the case) time is the same. Just more difficult to prefilter and clean as the filters may have to be on the bottom, and return pump on top (where it could run dry). If designed for this purpose, it would be the same.
To increase dwell time and saturation you ahve to slow down the return pump or enlarge the sump.