Well that was easy. Took longer to check out at home depot (buying a long phillips head) than to do it. There were rocks - not sand, rocks - stuck in the round outer piece of the impeller. Poked those out, gave it a rinse, and it fired right up. The BB is all dead, but that's OK. I'll just run another filter for a month with it and the other FX5. Gave me a chance to rinse all the muddy crap out of the bio media so the fish are better off for it anyway. And wow what a difference in flow.