This morning I happened to be outside when the pump started and a HUGE amount of air came out of one of the pool jets. It was like a giant "blurp" and then smaller bubbles continued for about a minute. I know I must have air in the system, but where should I start looking? The pump strainer basket has no bubbles other than the one that always forms at the very top of the lid. So I don't think it's the O ring. Suggestions?