Have alot of movement on the surface and a surface skimmer to remove any film on the water.
Roughly 3600L/H spread over 4 waterpumps in a 540L aquarium.
My tire track30+ inch-Has done this since around the 15 inch mark----It is perfectly normal for them to do this-I have a piece of black PVC pipe that is 4 inch in diameter for mine---And he still does it....