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

Air bubbles coming from the returns in a swimming pool may indicate that there is an issue with the hair/lint strainer lid not being secure or that the gasket has been damaged. When the lid is not tightly secured, or if the gasket is compromised, air can enter the system, creating air pockets that become visible as bubbles when the water is returned to the pool. This situation often occurs because the pump is drawing in water but can also inadvertently draw air, particularly when the lid is loose or the gasket does not create a perfect seal.

In contrast, damage to the return line from the filter may cause leaks or reduced water flow but is less likely to introduce air bubbles directly at the returns. Missing coping stones might affect the aesthetics or structural integrity of the pool edge, but they would not typically cause air to be entrained in the water returning to the pool. Lastly, while a damaged return line cover could theoretically allow for air to enter the system, it is more common that issues with the hair/lint strainer are the primary cause of air bubbles, as they are directly part of the suction side of the pool circulation system.