I have virtually given up on these pumps.  I have 4 of them.  1 nano - no probs.  Bought a 750 works sporadicaly with no logical sequence of when it wants to function or not.  Bought 2 larger evolution pumps from fellow club member - same thing.  I gave vinegar bath and same issue.  Was using the 750 the other day (it was working)....had it running for about 3 days.  Go to take it out of one tank and place in another - unplug...wait a bit....take out....put in new tank...plug in....nothing.  There is a slight vibration/hum indicating the pump wants to work....but nothing else.  Unplug, inspect, propeller appears to spin freely...assemble again - doesn't want to spin.  Try placing gaurd on different ways, same result.  I am using these for straight ciculation - no wave makers and not turning on/off frequently.  I have over $100 worth of pumps laying on the floor....ready for the hammer.  Any advice for a frustrated reefer?

Well...so far I am 1 for 3 with getting these pumps to work.  The 'stick the pen inside' method seemed to work for one...although not so much for the other 2.  Not sure what to do with the other 2....hang on to them...or toss them.  Such a waste.