Cardinal Has Lost Its Tail Fin

Hi,

I bought some green neon tetras (related to cardinals) a while ago to add to my shoal, and they all developed a patch similar to the one in your photo. Being aware of something called neon tetra disease, I euthanased mine straight away on the better-safe-than-sorry principle, so I don't know if it would have led to them losing their tails.

Since then I've read of someone who had a similar problem and they successfully treated it with an antifungal. You could try doing that, I seem to remember this person said it took a while for it to get better but it did eventually.

If I'd known that before my fish had the white patch...........