I have a 150-lb Hayward sand filter with brand-new sand, a dual speed jacuzzi pump (220V single phase, GE motor, rated 2-1/4 HP). This pump motor has two operation modes, a high-speed and a low-speed mode. When it is run in low-speed, the pressure drop across the sand filter is 2 psi. When the pump is run in high-speed, the pressure drop across the sand filter is 15 psi.
My question is, is the water being filtered if I run the motor in low-speed mode? is the filtering any better if I run the pump in high-speed mode? I like low-speed since its quieter. I am concerned that 2 psi pressure drop across the sand filter is such as small amount that I think water isn't really being filtered. Please share your advice.