My TDS is reading 1PPM after DI. Previously, it would read 8-10PPM after RO and 0PPM after DI. I have made somewhere around 200-300 gallons with this media. I know the DI resin is color changing, but what color is it supposed to change to? Is it time to change my DI or is 1PPM TDS acceptable? My tap is anywhere from 250-350PPM, if that's relevant at all.