It's very hard to know, without seeing the fish, I'm sorry to say. But the very first thing to do for any fish that's sick is a large water change. Fresh, clean water is the best friend any fish will ever have. read more
Carp are the only species of fish I’d advise this for, and the fish has to be willing to eat. I prefer to use brine shrimp or mosquito larva or daphnia for this purpose, as they are more natural, but peas have sometimes worked for carp. read more