I recently replaced my filter and pump and have noticed air bubbles (particularly at pump start up) in my return lines into the pool. This obviously implies a suction side leak which I have had before and was previously able to locate and seal a connection. This time, the strange thing is that I am not seeing any air bubbles in the pump basket. Just air bubbles in the pool from the return lines. I have turned the main drain off and still have the air in the returns. I have turned the skimmers off and the main drain back on and still have the bubbles in the return. In each instance I am not observing any air bubbles in the pump basket.
Any ideas? Is is possible to be sucking air into the pump without being able to observe bubbles in the pump basket?