Unknown COD for pygmy corydora

[chl0wning]

I was cleaning out my tank today when I noticed one of my pygmys wedged underneath a rock with a red dot on his belly. I had some pygmys that have had the red dot bacterial infection(?) before and i’m not sure if this red dot is a sign of that or if the cory just wedged itself underneath the rock and passed away. I tested my parameters and noticed that I had a higher pH of 7.6 so I put some neutral regulator in to tone it down thinking it was that? But ammonia/nitrates/nitrites were all normal. If he did have a bacterial infection, what is the cause and how can i prevent my other corys from passing?