Sponge filters are mostly used to capture large particles in SW
aquariums. Usually you will see them on ph to keep fish/inverts from getting sucked up in them. You also find them in HOB
and canister filters mostly to capture larger particles before it goes onto the next media.
Sponge filters do house bacteria that converts the nh3
but if not rinsed frequently (weekly) then the waste that builds up on them which increases your no3
. You want to rinse them in SW
not fresh/tap or else you could kill off the bacteria. Easiest way is to rinse them out when doing your weekly pwc
in the old water.
If you can avoid using sponges I would since they can be a pain to keep clean and will elevate your no3
levels. A skimmer works much better in removing DOC
and since it traps the waste outside of the water (in the collection cup) it will not increase your no3