RO/DI filter replacement

FB · 11/12/2007, 01:34 PM

Input TDS - 125
RO output - 24
DI output - 1.

I just changed my DI. I was just wondering how to determine when you change the RO filter.

Thanks

FB

AZDesertRat · 11/12/2007, 02:46 PM

Try testing it again. Get a squeaky clean clear drinking water glass with absolutely no soap residue or water spots on it. Let the RO run for 5 or 10 minutes to make sure any TDS creep has passed.
I first test the tap water TDS, then triple rinse both the meter and glass with DI water. Next test the RO only TDS beofe DI. Again triple rinse with DI. Finally test the RO/DI TDS and after a final rinse put the meter away clean and capped and place the glass upside down so no dust or salt spray gets in it so its clean for next time.

What membrane do you have? If its a Dow Filmtec 75 GPD or less then from a properly functioning membrane you should expect to see a 95-98% reduction in tap water TDS, or a RO only TDS of 3-6 in your case. If you have a 100GPD Dow Filmtec you should still be getting a 90% reduction or a RO only reading somewhere around 12 or 13 tops. If its still higher than that you have problems, it could be a bad membrane, housing, or even a dislodged membrane.

11/12/2007, 01:34 PM	#1
FB Registered Member Join Date: Jun 2006 Location: Georgetown, ON Posts: 1,305	RO/DI filter replacement Input TDS - 125 RO output - 24 DI output - 1. I just changed my DI. I was just wondering how to determine when you change the RO filter. Thanks FB

11/12/2007, 02:46 PM	#2
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Try testing it again. Get a squeaky clean clear drinking water glass with absolutely no soap residue or water spots on it. Let the RO run for 5 or 10 minutes to make sure any TDS creep has passed. I first test the tap water TDS, then triple rinse both the meter and glass with DI water. Next test the RO only TDS beofe DI. Again triple rinse with DI. Finally test the RO/DI TDS and after a final rinse put the meter away clean and capped and place the glass upside down so no dust or salt spray gets in it so its clean for next time. What membrane do you have? If its a Dow Filmtec 75 GPD or less then from a properly functioning membrane you should expect to see a 95-98% reduction in tap water TDS, or a RO only TDS of 3-6 in your case. If you have a 100GPD Dow Filmtec you should still be getting a 90% reduction or a RO only reading somewhere around 12 or 13 tops. If its still higher than that you have problems, it could be a bad membrane, housing, or even a dislodged membrane.