Purple tang with Ich or velvet?? What to do?

[Jtfortune3]

So I purchased a purple and yellow tang and added them at the same time 125 gallon tank. I noticed a few days later some dots on the purple.. they are both eating well and not flashing like many do with ich.. it went from just a handful of dots to ALOT!! I’ve run ichX for the past three days at recommend dose and just did 30% water change and added carbon.. could the meds be stressing the fish out more?? The LFS told me they had that fish for awhile and he would probably be fine if I could keep him eating... the tangs don’t fight but I can tell the purple is the dominant one and chases the yellow sometimes. (9 fish in tank) Nothing else in tank has signs of white dots...

 

[Jtfortune3]

I understand I have whatever this is in my DT tank now which is my fault but I don’t have any corals in the tank so I can use anything just fish safe to treat the tank.. pics of the tank and more of the tangs BEFORE the ich got bad

 

[bevo5]

I am by no means an expert but I’d do a freshwater dip as a first step.

The issue with treating the tank is that keeping a consistent copper level is going to really tough with all that rock work - so hopefully someone can offer a suggestion. If It were mine, I’d remove the fish and put them in 2.0 copper power and let the display sit fallow for the full 74 days.