Have an in ground gunite pool with 2 skimmers and 4 jets. I have my timer set up to come on at 9:00AM and off at 7:00PM. Each day when the pump turns on, air come flowing out of one of the jets. This last for maybe 5-10 seconds and then not another air bubble until the next morning when it repeats itself. I don't seem to be loosing water. Any idea where the air may be entering the line or why this is isolated to just one jet? Thanks.