GHA- Isolated patch, but need it gone!

Hey Everyone,

As many of you know, I transitioned from my 2 tanks to one 46g. Before the transition, my one tank had a major GHA problem and I decided not to use any of that LR because of it. However, I had a small zoa colony that I transferred and it had a small patch of GHA with it.

I figured that the new tank would take care of it as the water params would be more stable (larger tank) and I would be starting with 0 Phosphates/ nitrates.

Well, it is actually growing and I want it gone because it is starting to overgrow the zoas. I can't remove the small piece of frag because it has now grown onto the actual rock and I don't want to pull on it because of the zoas releasing toxins.

Any thoughts on a way to get rid of it without harming the zoas. I am looking for a short term fix.

I know that everyone will probably say to just find the underlying cause (which I am currently trying to figure out). I don't know if I am over feeding or if my RODI water is tainted. I just replaced my filters/ DI canister this weekend and I have a TDS meter coming tomorrow or Wed. So I'm going to find out if it's my water.