Hi All, i've a Pure Freedom Van mounted set up with a couple of 20inch pre filters & ro unit and di vessel. Only using 2000 litres a week at the mo. I had great TDS levels for a ages then as they crept up I changed the resin. After a couple of weeks this started to creep up again and now a reading of TDS reading of 10 Just trying to troubleshoot really. I'm getting a reading of 32 before the DI vessel. Is this good or bad? How often should the pre-filters be changed. I've ordered some new ones though some confirmation on what readings should be throughout the system would be appreciated. Tap water 272 down on the South Coast.