my cories always glass surf especially in the evening any reason they do this they are in an amazon biotype 50% weekly water changes just some tetras in with them in a 50 breeder there are 6 of them 2 large Amazon swords and some bogwood
It’s normal. They do this a lot. Sometimes they will dart all the way to the surface for a quick gulp of air.
The group I have will do this and usually within a day or so lay eggs on the glass