My sand filter has written on the tag that it takes,"1.6 cu.ft. media" (sand). How many 50 lb. bags is this? I just added three 50 lb.bags and my pressure (after backwashing) is approx.13-14psi. I had installed a couple solar heaters (black plastic roll-up type) yesterday (with 60 ' of plastic 1 1/2" pipe) and the pressure is now approx.20-21psi (in the "red" zone on my gauge where it reads "service filter"). It has a brand new Hayward 1 hp pump. Maybe too much sand in filter canister? What is proper pressure with NO solar heaters. What is proper pressure WITH solar heaters? Thanks All !