Hi again. Try a little dye first. With the pump off and the water very still, very carefully put a couple drops of a dye in the suspect area and see if it gets sucked in. You can use food dye (expensive), phenol red (the pH test liquid)...also expensive, or get a raw beet at the supermarket, chop it up and boil it, then eat the beet. Makes a bunch of deep red dye. You can use a basting syringe to slowly squirt the stuff.
Al