75 gal 2 month old Aquarium-UV Sterilizer?

Well, if it's Ich, which is what kjc2001 is asking about, the critical stage which any medication, hypo or UV will be useful is in the Tomite Stage (free-floating) which lasts anywhere from 1-3 days. Your tank should have cycled thru the UV by then. Reproduction of the parasite is much longer, like 2-4 wks.

 

You can put 1 of each tang in there, The blue tang is more vulnerable to Ich than the yellow.
I have had 3 tangs in my 40 for over a year with no probs, just dont put more than 1 of each type. I would soak food in a garlic additive to boost thier immune system.