I have a 1.5hp Hayward pump and a Triton sand filter. The sand filter is pretty big and has the clear bubble and pressure gauge on top so you can see the water in it. I just recently noticed that all the water in the sand filter is draining when the pump shuts off. When the pump turns on it has to go through the process of filling the sand filter back up with water. When it gets filled up (usually 2 to 3 hours) everything runs fine untill the pump shuts off. Then the water drains again.
Here's the crazy part. I don't know where the water is draining. I've checked everywhere (all around the pump and sand filter, backwash line). The only thing I can think is the water is draining back into the pool. I can hear it draining in the pipes. It is making a chugging sound.
The pump seems fine. The basket right before the pump is holding water and pressure just fine. Even when the pump is stopped.
I'm at a loss. Any ideas would be greatly appreciated.
1.5hp Hayward Pump
Triton Sand filter