Noticed 2 of my 3 male rainbows looking kinda rough today during a water change (pics are below). Their symptoms don't appear to be related, but I pulled them both and they are in Qt together.
Water parameters after the water change are ammonia 0, NitrIte 0, and nitrates 40 (higher than I expected after a 30% water change). No new livestock, plants, or anything have been added to this tank for months - the last addition was these rainbows which I bought as fry. They stayed in quarantine for a few months cause they were too tiny to go in the main tank and not get eaten. Tank is about 35 gallons and has been established for about 5 years.
Fish #1 has some sore, dark/reddish spots on his body. There also appears to be a hole in his side. I can't really tell if this is an internal or external problem or if it's bacterial or parasites. From the side the areas seem to be a bit raised or swollen. Both sides of his body are affected.
Fish #2 can't seem to close his mouth. He was also listing a slight bit, altho he's not doing that now in quarantine. He has no sign of the problem that the other fish has. Neither one seems to be at the surface gasping, either in the main tank or the Q tank. Both were staying apart from the rest of the school though, especially #2 with the mouth problem.
I have antibiotics, internal parasite and external parasite meds, but am not sure which to use. I'm thinking the antibiotic but I'm not sure if the first fish looks like a parasite issue or not as I've never dealt with parasites before (the hole in him is what makes me think possible parasites, altho that could be an ulceration too).
FISH 1 WITH THE DARK AREAS
FISH 2 CAN'T CLOSE HIS MOUTH (the cloudy areas in the last pic are water drops on the glass not something on the fish)