What is your input ppm? To lower you might need to fiddle with valve to get it optimal for current temperature of water. No figures for waste vs product flow make it bit more difficult deal with. Example if your running 50/50 ratio backing up valve and changing it to 60/40 will offer slight improvement. Some membranes struggle to get below 10 if input is high ppm. Alternative involves water softener as it tends to work better.