there are a few invert safe meds out there but i wouldnt advise any of them they havent worked in the past for me. remember no matter how great everything seems to be going do NOT add any other fish until one month after the LAST time u saw any kind of spot resembling ich, and to be safe give it another two weeks. tangs and other scaleless fish are very susceptible to ich and it will kill them quickly, so be patient and get rid of that crap.