They do spin easily when I check them with my hand. I have replaced the cartridge (the carbon-filled one). It doesn't spin whether the cartirdige is new, old, in, or out. I think it may have something to do with water flow, but I cleaned out the filter as best I could, even blowing out the uptake tube. it worked for a few hours after clearing out the uptake tube, then stopped again. There doesn't seem to be any certain fin that's dirtier or heavier than another, it just won't work. one guy at the
LFS said that it was probably just that it's so weighed down with bacteria that it won't spin and that it's a good thing, but I'm not sure the water's even touching it. any other ideas? I've got the bio-wheel just free-floating in the tank for now hoping that will work and I've been slowly moving the fry from this tank back into my community tank until I can get this figured out.
Any recommendations about what to buy if I just can't get it to work? The AquaClear HOBs sound the best because they use bio-balls instead of bio wheels so I don't have to worry about them not spinning or losing contact with the water, but wondered if anyone knew of something bettter.