Hello!! I have 2 comet goldfish who are both 6 years old and I think they are diseased. I don’t know what they have, but I noticed it about 2 weeks after introducing a pleco fish that I didn’t quarantine. (I didn’t know I was supposed to at the time . One of my comets became lethargic and was staying at the bottom a lot. (Started 4 days ago.) Its tail has begun to turn a rust color and the top of its spine has started to turn pink. It also swims around erratically. My other comet isn’t as affected, its color has stayed the same, but it has also begun to sit at the bottom of the tank. I at first thought it might be ammonia poisoning but my water parameters are okay. I have the two comets in a quarantine tank right now and my new pleco in another. My pleco isn’t really moving and isn’t eating. My comets will eat and swim around occasionally, but they just keep going to the bottom for 90% of the time. They seem to be taking shallow breaths. I’ve been medicating them with safeguard broad spectrum just since I don’t know what is wrong, and using aquarium salt. I thought maybe ich but they don’t seem to have white spots. I also haven’t been changing the water since I started the medication 2 days ago. Any advice would be great since they don’t seem to be getting any better. I’ve grown attached to my little guys and want them to make it.