A couple of my fish do this now and then like they are trying to scratch or something. Or are they playing? What I mean is: They very quickly accelerate the side of their bodies into a hard surface.
See tank blurb for tank info.
Set up for about 10 weeks.
No live plants.
Eheim Classic 2213 filter.
No direct sunlight. Darker room.
Water changes: 2 every 3 weeks. Bout 30%.
Feed once a day.
All test are very good.
Recently lost my first 2 fish: a rosey barb and a black platy, but they hadn't been doing this "scratching" thing.