I know is recommended, but the setup I have is having some issues with allowing it to tumble. What I have is a round fish bowl inside the return section of my sump and that is where the cheato resides. I have a Koralia 1 to make it tumble and at first it works well while the ball is small, but as it grows and spreads out, it catches in the K1 and just sits there. I figure I could thin it out but I think it would be better to have a larger ball, am I right? If a small ball works about as good as a larger one, then I wil take that route. But just wondering if the cheato is OK to just sit still with water flowing through it?