how should I polish water

[qwiksilver]

For best results, filter floss should be at the end of your sump, right before carbon, that way it has the opportunity to get the smaller particles you're talking about. It should go:

coarser foam, finer foam, filter floss, carbon (purigen is a better option, not only because it is rechargable, but because it leaves elements in that carbon pulls out).

This type of setup would ensure each section is maximized according to what it is meant to do. HTH