PM sent, but I'll post here for the forums sake. I left the sponge in the first chamber. The 2nd is empty for now. I rigged up some white LED's over it and am going to put some chaetomorpha in it. I don't know if it will work out, but I'm going to experiment. The 3rd chamber is filled to the brim with live rock rubble. Nothing but the return pump and the heater are in the last chamber. So all my filtration is natural. I have a total of about 25 lbs of LR including the stuff in the back, so that alone takes care of it. I also have around 25-30 lbs of live sand. The sand bed is around 3 1/2- 4 inches deep. Not sure if this is really a deep sand bed, but I'm guessing it does some good. I've had no problems (with the exception of my clowns which got ich) and all my corals are looking nice. My parameters have all been good too. I'm not using the bioballs, ceramic rings, or the carbon that came with the setup. I'm guessing the stuff that came with the tank would be fine for a fish only tank, though. I've heard that the bio-balls can produce a lot of nitrates though. I don't know if my setup is the best. I'm sure it can still be improved, but it's worked for me so far.