I doubt copepods are "fogging up" your glass. They are sitting on the glass because they like the biofilm that is growing on it. Usually it's a mix of bacteria, diatoms, and other organisms that populate clean surface area fast.
If you can manage to get decent photos (macro lens could be enough, but microscope would be better), we can see if there is something you have to worry about, but probably it's fine.
Munnidae isopods are a bit larger than copepods, maybe that's what you are seeing. I also sometimes see
Tanaids on the glass (but rarely as they prefer staying in the substrate)