I grow tomatoes for market in a 60 bucket recirculating system. the plant are in netpots of lava rock and the roots just hang down in the water. My water comes from a shallow groundwater well and come out at 600 to 7oo ppm as measured on a Hanna Primo which calibrates at 1382.Last summer I ran a diatomaceous earth swimming pool filter ahead of a small 100 gpd under sink unit.This would make about 30 to 40 gpd for about a week until it would finally go to nothing at which time I would have to replace all three filters plus the ro membrane.I am in the sea islands and dirt here is just sand and this well water is tasty and doesnt have any red color to it so I am assuming the minerals are mostly cal mag. Anybody have any ideas? thanks in advance. Happy Hydro