no-ich shelf life

[eleyan]

My blue tang got ich a few days ago. I've had it for 3-4 years and the tank has been stable all that time. I just added a couple of new fish right around the same time it started showing the white spots. None of the other fish in the tank looked like they had any spots, so I was hoping that the blue tang will be able to get over it. I started adding garlic extreme and marine-C to its diet. Today however, I noticed that it had more spots and some of the other fish started scratching their selfs.
I have half a bottle of no-ich from about a year and a half or so ago. Does anyone know what the life shelf for that stuff is?