One of my discus is sick It’s dark in color, has an excess slime coat, and has one clamped fin. It won’t eat either. Yesterday I noticed that it had a clamped fin, so I did 90% water change. And it was better afterwards (literally it was eating and acting normal) I’ve had these fish for almost a month with no problems till now, I change the water everyday, at least 60-75% It’s a 50 gallon tank, and stocked with 5 discus including the sick one. I’m not sure what’s wrong?