Bosemani Fan said:First make sure it is seated in the holder good, If its not in the slots exactly as it should be , It will not turn good at all. Also you need to swish it around in the tank every 1or2 weeks, and that should help clean it off when it starts getting gummed up with all that good Bacteria. If you have to you could Spray them off in the sink using Tank Temp water. But you should never let it stop long enough to dry up.
I use two Bio Wheel filters, and mine constantly turn ..., or forgot to remove the piece of paper that comes wrapped around it.
The wheels will also stop turning if the carbon filter behind the wheel gets messy. It's all a flow thing -- the water must be coming down the shoot with enough volume to hit the impellors on the wheel -- gumming up the floss in the carbon filter will lower the volume that gets to the shoot and the wheel will first start to spin irregularly and then it will completely stop.