One of my corydoras has a small dark spot right by the “flap-like” covering of its gills (I don’t know the proper terminology). I’m not sure how long it’s been there, but I noticed it probably around 2-3 weeks ago. It’s not exactly a spot on his scales but almost more like a very small peice of something attached to him, I will put s below. I don’t know what it is but it is slightly frightening to think it might be adome sort of parasite or something. At this point he has been acting completely normal as far as I can see. I’m not sure what to do, any advice would be great. I’m just worried if I treat him for something that he may not have, it may make him feel worse, but also if it will end up harming him, I would want to be proactive (I also have 4 other cory catfish, 1 gouramI and a mystery snail if that’s relevant) . Thank you for any advice.