Have a 55 gal with fair amount of coral and few fish. Huge wet dry filter and backpack skimmer. Can keep the nitrates below 40, but need to do water changes every 4 days to do so. I thought i had too many fish, but have been told this is not the problem. Have medium hippo tang, small lawnmower blenny, flame hawk, marine catfish, six line wrasse, and yellow head sleeper goby/sand sifter. Coral includes xenia, one open brain, small gorgonian, some zoa's and star polyps, black and red sun polyps, shrooms, finger leather, spagetti, and medium bubble tip anemone. I know people keep tanks with much more and keep the nitrates down. Have 2 large balls of spagetti macro algae. Any suggestions would be nice. would like the nitrates to stay below 10. thanks