Hello, I have a cory cat that has been healthy since I got him over 2 years ago. However, a couple of months ago I noticed a white 'dot' on his head, about the same size as one of his eyes. This has gradually grown to about 4x the size of his eyes, and it appears the skin is simply deteriorating away (the attached pics were taken today). The little guy has so far shown no signs of distress, and continues to eat and explore as usual. I have searched images and threads all over the internet but so far have seen nothing that looks like this. My water is healthy, I do regular water changes & gravel cleaning (usually twice a month, but I've done cleanings twice a week since discovering this issue). I have 18 fish in a 45g tank, and all of the other fish are doing great with no visible signs of disease or distress. So far I have done no medications (the last thing I want to do is medicate for the wrong disease and end up stressing out or killing other fish), but I would love to know what this is and how to effectively treat it. Has anyone seen this before? Does anyone know what it is? Any help would be most appreciated!