Treat with hyposalinity - it works if you follow the instructions to a T.
I did it once for my 90 gallon display tank and it saved my fishes life.
I am now doing it for my fairly new 120 tank setup that has ick.
I know many people setup QT tanks for treatments. However, I find that to be more stressfull for the fish.
I simply remove the live rock, in escense QT the live rock so you don't kill it. The live sand will die, but it will regrow afterwards - no biggy.
My guinea fowl puffer is about 10 inches and my triger is about 6. I can't see putting such big fish into a qt tank. I think it causes more stress for the fish to move them out of their familiar suroundings than to remove the things you want to preserver and treat them with hypo int he main tank. I won't use copper because you can't get it totally out of the tank if you do use it. So I just use Hypo. Beth taught me well when I encountered the issue when I first got into the hobby. It works and it is the only thing that does work without question. I do the hypo treatment routine in display and watch params carefully. Particularly ph which drops from all the change over to fresh water. My main display tank is at 1.010 and ph of 7.6. The ph is a little low so I added some buffer, I might add an auto drip of it or kalk for a while. But they will ride the hypo for a full 6 weeks. And then the rise back up in salt needs to be done very slowly.
I would start treating with hypo asap, whether it be in your main display or in a qt - but get it going soon cause ick can take down a fish fast.
I wish you the best. Ick is evil. KILL all ich.
