Here is what I would do. Do a water change, pull the sponges and rinse them is the water change water. Squeeze them until you don't see junk draining. Stick them back in and monitor your
nitrates, keeping track of the days. As soon as you see the
nitrates creep up even a little you know that you have nitrifing bacteria built back up in them and you will know that you should rinse them at least a day or 2 sooner.
If you don't want to go through this I would rinse them at least weekly and monitor to see if the
nitrates drop. I know that some people use filter floss or pads that they just take out and throw away. I pulled the sponges out of my nano's rear chambers and didn't replace them with anything.
I also unplug my return pumps when I feed so that it is less likely that food gets pulled into the
sump or rear chamber. I leave the powerheads in the
DT running so that the food stays suspended for the fish and corals to find. I only put a little bit of fish size food in at a time. As long as they attacked the food with vigor previously I give them a bit more as soon as it is all gone. Once I have given the fish a couple of helpings I target feed the corals that need meaty foods. I put all the small coral food in at once. When feeding corals I leave the return off for about a half hour so the corals have time to catch the food.
