My Incoming Water was 120-150 tds depending on weather conditions.
Outgoing after my Merlin with booster pump at 55 psi was 20-28 tds.
Mine was affected by low volume of available water as well as low pressure.
Without the booster pump it wasn't enough pressure to open the inlet valve.
My mates same set up with incoming at 300 tds, fed to Merlin input by 1 inch bore hose, so tremendously high volume of water available, through booster pump at about 70 psi produced an outgoing merlin product of around 11-15 tds.