Funny thing, after absence of some time when I returned to the hobby a few years ago I bought into the bio wheel concepts. I got the 450's and they worked great initially. But over time, I too, found that the wheels would slow and only turn occasionally then the wheels stop turning completely. Even though I had cleared the axles and made sure the tubing was all clean....eventually the intake piping and the spray wheels would stop moving water too. I suspect the issue with the bio wheels is that they would collect debris/materials in the folds. Such that there would be too much weight in some folds of the wheel material. Resulting in the wheel being the weighed down and not enabling it to turn. And then I had issues with the plumbing. IMy flow adjuster, if closed water would not flow to the spray pipes. Ultimately I had to completely tear down the 450 and now it's working, but certainly not like it did when new. On another 450 I had the same wheel issue but the intake piper would not seat correctly so there was always noise from the impeller. That unit was ultimately sent to the recycle bin. The good news is that I think my issues have to do with the fit, finish, and engineering. The units gave great performance for the first two years or so but rapidly went down hill after that. I still have 1 450 but now using bio balls and filter floss. I've given enough money to Marineland. With all that being gripped on it does appear that the new PRO versions have been redesigned for the better, but I'm now a SeaChem Tidal fan.