I'd already checked out some of the links you listed, and I just looked through the others but saw nothing that looked like my problem.
My tank is 55 gallon. It has 4 angels, two silver dollars, 2 tiger barbs, 4 rainbows, 2 sharks, 1 loach, 1 otto, 2 little frogs, and three gouramis. All of these are juveniles except for the silver dollars and Angelly, the fish with the spot.
I've had Angelly for almost a year. I did add one new fish, a small yellow rainbow, to the aquarium about a week and a half before the spot appeared. I've never fed anything but NutraFin Max and freeze dried bloodworms.
I use a python to vacuum the gravel, changing 25 to 30 percent of the water every weekend.
My water parameters are:
The ammonia and nitrate readings are both slightly higher than usual. I didn't clean the tank this past weekend due to treating with Parasite Guard (which hasn't done anything at all yet.)
Today my LFS
recommended treating the entire tank with Copper Safe, but I've heard that this can be harmful in the long run; and I'd like a second opinion before starting something like that.
Angelly still acts like nothing is wrong.
Thanks for the help,