I have two pearlscales, one black moor, and a panda butterfly in a 40 gallon quarantine tank. No ammonia or nitrites, 10 nitrates, temp is 72.5 and pH is 7.5. They have been chasing each other in circles and pushing up on each other's stomach, seemingly in an aggressive way. There was been no known injuries, their fins aren't shredded at all, but I worry the constant pushing around may stress the fish. Does anyone have any idea of what may be causing this behavior and how to make it stop?