Welcome to AA, the best dang Aquarium Advice index anywhere!!!!! 8)
Now to business...
How large is the tang? Your aquarium can hold about 5" of fish TOTAL, and not counting the tail fin. Your tang either is, or will get too big for that tank, I believe, because they get up to around 8". I realize that that he's a survivor so far, but I think leaving him in there is making one very unhappy fish. If you can get store credit at the LFS
, you might consider taking it, and giving the aqaurium time to cycle.
The cycle is the processof growing the proper bacterias needed to break down organic wastes so that they will not produce toxins......it does to the water what trees do to the air, sort of. How did you set up the tank? Did you use the same water? Did he/she give you the sand that was being used? What all equipment did you get? What filter, powerheads?
I'm also worried about the effects that such a low ph
has had on the tang. What was the salinity before you got it to 1.022? Sorry for the drilling, but we're going get you in the right direction ASAP