pump losing prime, low suction pump basket

[lbloom]

I have a 15,000 gallon " on "ground pool with what I'm told is an above ground pool pump that is above the water line. It has been this way for years even though we replaced with duplicate pump this summer. We currently aren't able to close the main drain to vacuum due to the pump losing prime when we try. I have good return pressure. Pool is cloudy. Could this be due to dirty sand filter? Sand is at most 2 years old. I understand the first thing people will assume is the location of the pump but as I stated it has worked with this set up for years. I'm at a loss