Weighted hose, but that pull down can't be any stronger than the lift up when the diffuser swells up with air. It couldn't have frozen due to depth underwater. I kept it deep all winter, just didn't run it.

Since there are only 2 of us with the problem it is likely just a rare defect. That pvc is thick and under any normal use should not break. I know mine was not abused so the logical explanation is a defect in the pvc. What caused it to finally give out after a year underwater is another question. I was just happy that the membrane wasn't blown out. Pvc is easy to fix or replace.