Here are what I see to be your problems:
- Your skimmer sucks. I think it's the worst "mainstream" skimmer on the market. Unfortunately, it's sold in a lot of stores, so a lot of people buy it. You basically bought a $120 powerhead. Keep the pump, throw away the rest of the thing. The SeaClone is an *okay* skimmer for a 35 gallon tank with 2 fish. But a 90 gallon tank with 11 fish? You may as well not have a skimmer at all. With that bioload, you really need to get a good skimmer, rated for double your tank size. The Octopus brand are the best on the market now, in terms of affordability.
- You have crushed coral substrate. Crushed coral particles are large enough to trap detritus and crap, and not small enough for your cleaner crew to keep clean. People with crushed coral often see nitrate problems. Removing the crushed coral and replacing it with aragonite sand is what you'd have to do to fix this, but that solution is tough to carry out, and when you disturb the crushed coral you end up releasing all that crap into the water column anyways. If that's what you want to do, then I believe getting rid of the crushed coral will really help. If you don't want to take the risk of stirring up that muck, you'll just have to find a way to remove the nitrates instead of fixing the cause. See my point about the skimmer above.
- Tap water. Okay, it may test nitrate free. But it probably is filled with heavy metals and phosphates -- compounds that a water conditioner cannot remove. Using tap water is one of the worst practices you can have when it comes to maintaining your tank. You really really really need to either start buying RODI water from the grocery store, Walmart or your LFS, or you need to buy an RODI unit to make your own. RODI units don't have to be expensive. I bet you've already spent at least twice as much trying to fix your nitrate problem than a decent RODI unit costs. My RODI unit was purchased from
www.purewaterclub.com. It cost $60 + $40 shipping (5-stage, 100 gallons per day). Look into it. If your tap water isn't causing high nitrates, I bet it's causing other problems instead. Tap water is a huge no no for any saltwater tank.
- You feed flakes. Flake and pellet foods contain preservatives that lead to poor water quality (high nitrates and phosphates). Switch to frozen foods only. For your vegetarian fish, stick with frozen Emerald Entree, frozen Rod's Food for herbivores and dried seaweed sheets instead of the flakes.
- 220 ppm?!?! Are you sure something didn't die in your tank and you just haven't noticed? Did you ever, by chance, have a sea cucumber or any other animal that buries itself in the sand? If those things die in the tank while they are hiding out in the sand, forget about it -- your tank craps out. My nitrates have been that high before too, all due to a sea cucumber kicking the bucket. And if they die in the sand, it's pretty much impossible to get their bodies out, so they slowly release their toxins and rot into the water.
I think that's all :)
