Goldfish questions PLEASE ANSWER I really need help.?

well, goldfish (especially common/comet goldfish) get fin rot or tail rot from dirty water. If your aquarium is dirty at the moment, do a quick water change and give him the treatment needed. Fin/tail rot usually happens when the water is dirty. Live plants are good but not plastic, because they're sharp and might stab onto the fins. i once had a common goldfish it rotted it's tail all the way and it's fins are clamped to his body and it sank to the bottom of the tank. I knew that it might have swim bladder disease but it might not be swim bladder disease b/c since his tail is rotted he sunk below and kept getting sucked onto the hang on filter. so the next day it died. So always buy/choose a goldfish that is healthy with no diseases.