I have a JBJ 45 and one of my return pumps has a constant stream of micro bubbles being blown into the tank. I took the pump out cleaned it, made sure hoses were sealed tight, I have to pumps in same chamber only one is blowing out the air bubbles, water level is where is should be, checked the plastic fittings for any cracks that maybe air was getting drawn into and couldn't find anything.. Any advice?