At this point IMO
the sponges will be mechanical(or atleast I hope you know you will need to rinse them so they don't become large nitrate factories), and would say the filter floss suggested earlier is a better choice (again IMO
The area of a sponge to become biological is wonderful if that is what you use the sponge for.
I am the sponge guy(BIO IS BIO).
So if you will have to squeeze/rinse the sponge every week or two why not floss?
I don't run HOBs on any of my marine (all sump and all spoiled!) but I run many aquaclears on my freshwater and have filter floss on top of everything as last filter.
Really does catch some crap.
Throwing out weekly is easier IMO
then rinsing,and provides perfectly clean new media.
Good luck !