My 5g tank is a little more than 3 weeks into the fish in cycle (without testing kit). Some time ago I read about aquarium foam being used in the place of filter cartridges. If I were to do this, how would I switch from cartridge to sponge in terms of the beneficial bacteria? I have the Mini Might internal filter that came with the tank and I cannot fit both of them into the slot. Since I'm assuming my tank is not done cycling yet, should I wait to do this? And what would be the maintenance required for it (cleaning, replacing, etc.)?