i just started a 15 gal saltwater with 15lbs of live rock. i also bought a nice 3 stage filter with bio, sponge, and charcoal for a 30 gal tank that the lfs lady recommended. at the time i was not really aware of protein skimmers, but after reading tons of threads i notuice everybody seems to have one. all of their tanks are much bigger than mine though. so do i need to invest in one of these?