TDS question

[hoyt]

I just got my tds meter, my tap water reads 150ish ppm, my rodi unit gets it to 7, is 7 too high?

[AZDesertRat]

If 7 is after a DI filter ,Yes its too high. A good RO (75GPD Dow Filmtec) provides 98% rejection, so you would see 3 ppm TDS after RO alone without DI. After DI you should see 0 TDS for hundreds of gallons at least before starting to creep up to 1 or 2 before changing DI filters. If you have a 100 GPD 90% rejection unit your RO output should be somewhere around 15 but your DI should still produce somewhere around 150 to 200 gallons before changing filters. Thats if you have a large capacity DI filter and not one of the little horizontal types.
How old is your filter system, how much water has passed through it and what membrane and type of DI cartridge does it have? What are you using to hold the water you are testing, a clean glass is best. How long are you letting it run before testing? Regardless you should be getting better than that.