Should pool skimmer door flap be flopping?

No, the pool skimmer door flap should not be flopping. A properly functioning skimmer door flap should remain closed when the pump is off to prevent debris and water from flowing back into the pool. If it is flopping, it may indicate that the flap is damaged or not sealing properly, which can lead to inefficiencies in skimming and increased debris in the pool. Regular maintenance and inspection can help ensure it operates correctly.