This may be a stupid question, but I'm a new owner of a house with a pool. I've been regularly backwashing my sand filter after vacuuming (as per the previous owner's instructions). I've noticed that where the water comes out onto the lawn are small mounds of sand deposits. The sight glass is clear and the pressure is at 15psi (normal according to the previous owners). Is sand deposits from backwashing normal? I just don't want to drain the sand out of my filter. And I haven't noticed any sand in the pool (yet)