What should the PSI be for a 40x20ft. inground pool be?

The amount of water pressure or pounds per square inch (PSI) that should be maintained in an inground pool to keep it operating optimally is typically between 20 to 25 PSI for a standard concrete pool, and between 8 to 15 PSI for vinyl liner pools. It's important to follow the specific specifications provided by the pool manufacturer and your pool equipment retailer based on specific pool model type and region (weather considerations).