Lew- Im doing the same thing with my ro's for the same reason as you. Id like to have enough ro to single pass to 15% at six gallons per minute to match where Im running my evaperator. Pretty tall order though to do that. What Im going to do is run the 900 gph and the 1200 gph machines kind of open flow into a tank at say six percent and then Im going to fire up my cdl 900 and see how many gph of 15% I can make per minute that way. Im not sure what Im going to get. I also might churn out a couple thousand gallons per hour of water first off and then try my two step trick. Have to just experiment. I think I have a good fix on the high pressure pumps becouse Ill be running 17.5 hp of high pressure pumps for six posts and cdl says a 7.5 per three posts so I think itll work good. Whats the high pressure pump(s) on yours? Theron