I am running two bio wheel 350's on my community tank. On one filter I have put just sponges the aqua clear 70 fit perfect in there 2 on each side for a total of 4 sponges and the other I use a filter floss and a bag with a little carbon. I use the sponges just for the surface area as I have a decent bio load to keep up with. Will lava rock in place of the sponge work better? Or maybe 2 sponges on one side and lava rock on the other? Any ideas on what is better would be very much appreciated.