My Aquaclear 50 filter stopped working for some reason and I needed to replace the motor. I was looking for one and discovered that it's the same motor for models 20 to 70. Please see link. http://www.ebay.com/itm/NEW-AquaCle...251?pt=LH_DefaultDomain_0&hash=item3a7aef5863 Does anyone know if the impellers are different for the mentioned models? An AC 20 filter is cheaper at PetSmart ($18.87) than the replacement motor (Ebay $24.01). It seems to me that a smart move would be to buy the AC 20 filter instead of the motor. Or am I misinformed?