It really depends on stocking levels, and how much you are feeding. A planted tank should not ever be at 0 nitrates, because that puts the tank at a
It's Sunday morning schedule
It all up to you that you want to get the fry grow up into frogs or do not want any more dwarf frogs.
I doubt that slower flow rate makes any real difference, the bacteria actually cover just about every surface in the aquarium. They're not all confined