Question for anyone with experience with pincushion Urchins. I recently purchased a Purple Pincushion from my LFS on a Black Friday sale. I have a 125 gallon (6' long) reef tank. The one I have is doing a great job of cleaning but it only does almost exactly 3' of the tank in circles. Front glass, side glass, back glass, rockwork, etc but only on half of the tank. Do they have a very small territory or does mine just have short legs and not want to talk? I'm considering getting a club/mine urchin as well so I can always put that on the other side but it's just silly this one refuses to go west of the center of the tank.