I am overhauling my sytem and turning it into a fish/invert/liverock sort of thing. I have a 55 gallon tank. The only circulation and filter I have currently running is a large 350 gph protein skimmer. I have some live rock right now fully cured and about a year in the tank. It is an assortment of real rock and tufa rock that I seeded with the real. I also have about two inches of live sand. My question is this. with the rock being my only real filter how much do I need? Do I measure it by amount of space it takes in my tank or do I wiegh it on a scale? I plan on having about two tangs, a blenny, a domino damsel, and mabey a clown fish. I will also have hermit crabs and snails.