New addition? In your display or a QT? Just went through a bout of ich on some newly acquired clowns and gobies from petco, half way through the copper treatment now, lost a gobie early on from basic mistakes like not doing a FW dip to alleviate initial stress, not running low Specific gravity, etc. if your fish is actually sick and you plan to medicate it, check out humble.fish it’s a forum made by community member humblefish (active on many forums) that forum has priceless information on how to diagnose and treat sick fish. Research research research, and if you must ask a question give a decent background so you can actually get help and showcase that you have done your homework