Does my tank have the ich?

[newreefy]

I bought a yellow tang about 3 weeks ago and after a week or so i noticed some white spots on him. I read through previous posts and thought i would try mashing up garlic and soaking it up with nori and feeding it to the tang. I have done this for 4 days now and no improvement (just seems to be getting worse) my water quality is perfect. i also have green chromis that seem to be disapearing as well. The tank has 2 peppermint shrimp as well as hermit crabs and snails. What else can i do to try and cure the disease without harming the snail,crabs and shrimp. The tank only has live rock in it right now. Any help would be greatly appreciated