Hiya guys! Yesterday I picked up four corys and a snail and I currently have them in the quarantine tank for a week or two before I add them to the main aquarium. Thing is one of them turned out to be extremely weak. This morning he was incredibly sluggish and didn't look so good and then this evening he was struggling to swim with the others and then just kept sinking to the bottom and once or twice landed on his back before flipping over again. I took him out and looked at him closely and saw that he actually had some serious dorsal fin damage and some tail fin damage as well. I guess I must not have noticed that at the store. I put him in a separate two gallon fish container I have upstairs with some fresh new water but when I put him in he got stuck in a plastic plant and was too weak to free himself so I helped him out and then a half hour later he was just lying on his side gasping before finally passing away a few minutes ago. I'm not sure what exactly was wrong but I'm guessing if it wasn't the damaged fins it was a swim bladder issue or a combination of both. I think I even heard the lady that bagged him at the store asking herself if he was floating for a second or not. He was probably just a weak fish but that leads me to this question. Even though I don't think it was an illness should I do a partial water change in the quarantine tank where the other corys are? I did a change yesterday before I put them in and they all seem active, curious and perfectly fine so there's nothing obviously wrong with them but just in case do you think it's necessary to do a water change in case this cory introduced some kind of pathogen to the water? I usually do a change if a fish dies but again this particular fish died in a separate container, not the quarantine tank.