Need help with Disease ID!

Hi,

I am new here. Just recently started up a 125 gallon salt water tank. I have had it about 3 months now after the cycle. I have 2 Clownfish, 1 blue/green chromis, yellow tang and a blue tang. All of the fish Were fine for a while until I added a pepermint shrimp from a bad fish store. They used the same water for him as a fish that I could see in the tank had ich. I figured it was fine so I just brought home the shrimp not realizing that the water would have been contaminated also.

Shortly after my blue tang now has ich and has been showing some signs for a few weeks now. I tried a few options for the reef tank, but I do not have a qt tank so far.

I thought ich would pass by now, at least on the fish and go into one of its "multiplying stages" but it just wont leave.
My levels in the tank are all zero.

Now there what looks like a giant black spot in the side of him,


any idea what this is? Do you think I should try to take him out and put him in another tank?? or would that stress him out even more to kill him.

Thanks,

Adam