recommended turnover rate for 55 gal tank?
 

Hello,

I have 3-month old 55 gal aquarium that's heavily planted. I use an
automated CO2 system and everything is going well. right now the only
fishload is a small school of cardinal tetras.

anyway, I don't use any filtration, but would like to add a small
mechanical filter to get rid of the occasional debris and (rare)
surface film. I just want to use some floss or foam block and plan to
clean it every other day. I'm leaning toward a small Eheim canister
with the Eheim surface and subsurface extractor system. I like the
Eheim return bar that I can place well under the surface to prevent
surface agitation.

what flowrate should I be looking at?

thanks!