I just noticed this morning that my pencil tetra has something of an ulcer on it's body. I'm not sure if it's an ulcer actually, but it doesn't appear to be wound as there's no blood...it's a greyish patch on it's body.

I fear it may be a fungus attack and am afraid it might pass to the other fishes in my tank. As of now...it doesn't seem to be able to swim properly. It is not able to stabilise itself as it swims around...constantly rolling. I'm quite afraid to euthanise it, as I don't really know how to do it.

I just introduced 3 SAEs into my tank in the hope that they might be able to help me combat my GBA problem which has gotten out of hand...would it be possible that they attacked my pencil tetra, because it was fine yesterday before I introduced the SAEs?