I have a female P. regalis who keeps knocking one or more of her legs on the side of the tank. It's almost as if she has something on it and is trying to FLICK it off or it is itching her. I can't see anything on it (although it is hard to really get a good look) and I cleaned the tank a couple of times but she still does it. Has anyone had this problem before or does anyone know what is going on here? Thanks.