i have 4 jerdoni and only one them has these spots on the tail. it looks like a pimple but not even close.. seems like a bump with redish on the side. the fish eats well, not skinny at all. very active... but i want it gone before i join all of them to my big tank. just a precaution... i don't want my large tank to get any disease due to my ignorance. please help identify what type of disease it is... and any suggestion on what medication to use.. they are in a community tank with loaches.

