So what you can do is increase your filtration. I would buy a bunch of bio balls or blocks to increase bacteria and add a refugium with a strong light and run it at night for 16 hours everyday. Keep feeding the same for the next couple weeks and with the added bacteria and fuge it should start bringing things down slowly. Buy a nice chunk of cheato though.I have a yellow tang, purple tang, and a hippo tang. So in total 3 tangs