I have a 75gpd BRS rodi system. Just changed my filters and di resin. First 100 gallons were at 0 tds. Second 100 gallons is now showing 4 tds.. 3 weeks into the fikter changr.. My town water is 400 tds. Anyone know what's going on? I read that you want to change the filters when you start getting readings over 4.. It's only 3 weeks old..