Teresa, I got your PM. If Dan weren't already in this thread, I'd probably be behind the scenes picking his brain for his experiences anyway. I defer to him in all things seahorse.
I do agree with Dan and Renee. It doesn't strike me as a standard pigmentation issue. I don't have any first hand experience with pathogenic ciliates, but some of them can be really tough. Uronema among them. Chloroquine would definitely be the go to med, and the only really useful treatment if that's what it is.
If you do a formalin treatment, which wouldn't hurt, I'd be careful doing it in the display. I'll go back and look through some things, but Dan would probably be better at giving advice on it. I know that you
can use formalin with cycled filters, but there are likely things in your display that will be negatively affected. Either way, definitely oxygenate heavily.
Also, FWIW, sounds like Beth is doing everything she can to help you out here. Hopefully she'll be able to get you some answers you'd probably never be able to get on your own.