What may cause air bubbles coming from the returns in a pool?

Air bubbles emerging from the returns in a pool can often be traced back to issues with the hair/lint strainer lid not being secure or having a damaged gasket. When the lid is not properly sealed, it can allow air to enter the filtration system, which then gets pushed back into the pool through the return lines. This creates the visible air bubbles that pool operators commonly observe.

Ensuring that the hair/lint strainer lid is secure and the gasket is intact is crucial for maintaining an airtight system. If either is compromised, it can disrupt the normal function of the filtration system, leading to the introduction of air into the water flow.

The other options, while they can create different problems in pool maintenance, do not directly relate to the introduction of air bubbles in the water returning to the pool. Damage to the return line from the filter might lead to leaks or reduced water flow, but it does not specifically address air entering the system. Missing coping stones could affect the pool’s aesthetics or safety but would not impact air intrusion. Similarly, damage to the return line cover might affect water return or circulation but is less likely to cause air bubbles compared to the effect of a loose or damaged strainer lid.