Every time I check the skimmer basket, I usually open the bleeder on the filter and there is always some air in there. I have the pump running for two 4 hour cycles per day and every once in awhile when it shuts off there must be an air bubble that comes back up through the skimmer and pushes the basket out and upside down (it has a scum sock on it). Is this normal or do I have air leaking into the system somewhere? There is usually no sign of air in the pump basket or coming out of the return jet when it's running, only in the filter. (24' round AG pool with pump/filter sitting on the ground)

Thanks

Peter