I’m quite new to the hobby. I have a 54ltr cycled tank with 8 male guppies and snails. A couple of months ago I lost 2 fish to an ammonia spike and a third survived but with massive loss of tail. He has been getting thinner ever since, still eats and swims but compared to his companions he is emaciated. He has no sores or obvious worms or fungus. My levels are not perfect, ammonia 0.5, nitrite 0, nitrate 10. Should I euthanise him in case he has something infection, or is it likely he just never fully recovered from ammonia poisoning?