[SalTee]

My Perculas have/had a white swelling around the mouths. One has gotten bad and is being treated in a quarantine tank- S.G. @ 1.011 and copper meds. The other's swelling has receded imensely and almostgone without treatment. What is it, is my treatment working, and is it strange that they both don't have it equally as bad. Side note-my hypothesis is a fungus.

[Ninong]

That sounds like it might be lymphocystis, which is a viral infection. If that's what it is, I don't think hyposalinity or copper will have any effect.

How large is the "white swelling?" Does it look sort of like a small wart?

[leebca]

Treating with copper in a hyposalinity solution is lethal to marine fishes. Please either stop the copper treatment or stop the hyposalinity. See: Copper - Treatment, Use, Problems

For the proper and best diagnosis, I'll need to see a photo of the fish(es) you are talking about. Swellings can range from viral infections like Ninong points out, fungal infections as you suspect, bacterial infections, tumors, organ infections, flukes, parasites, etc.

[SalTee]

Good news- it seems to be gone in one and almost non-existentin the other. When it was in full swing, they looked like Santa Claus fish. can't get a picture, sadly- camera isn't working. Thanks for the info!