This may be stupid but my return is blowing something into the pool and I can't tell if its just air bubbles or sand. The level in the pool is a little low so I'm hoping that air is just getting sucked into the skimmer and that it's just bubbles. I put a cup in front of the cup and then looked into the cup and saw no sign of sand. My question is could low water level cause the return to blow out a lot of bubbles?