I have mini Whisper filters, the internal kind, in my 5.5 and 2.5 gallon planted tanks. I recently stopped using carbon when I found out it would take the ferts out of my water. It seems like a waste of money to buy the filter inserts and not part of it, so is the something else I can replace the filter inserts with? Would it worked if I just shoved some filter floss in there instead?