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TDS and RO/DI

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NaH2O

Well-known member
Joined
Jan 25, 2004
Messages
8,568
Collin - I hope you can increase my knowledge about RO/DI water.

I posted the following several months ago, and I would love for you to correct any inaccuracies you find. My question is based (kind of) on the post/reading I did. Nikki's Post - any suggestions for RO units. I was explaining deionization to someone recently, and questioned myself about resin exhaustion.

My question is about TDS readings when DI resins start to become exhausted. Since it appears silicates are the first to leach through (?), would they show on a TDS reading? Are there other compounds that might leach through and not register on a TDS meter?

Thanks
 

cwcross

Well-known member
Joined
Aug 18, 2004
Messages
250
NaH2O said:
Collin - I hope you can increase my knowledge about RO/DI water.

I posted the following several months ago, and I would love for you to correct any inaccuracies you find. My question is based (kind of) on the post/reading I did. Nikki's Post - any suggestions for RO units. I was explaining deionization to someone recently, and questioned myself about resin exhaustion.

My question is about TDS readings when DI resins start to become exhausted. Since it appears silicates are the first to leach through (?), would they show on a TDS reading? Are there other compounds that might leach through and not register on a TDS meter?

Thanks
Nikki, this seems a wells studied and accurate write up. I would add that RO units separate based up size, or more appropriately, what is called hydrodynamic radius. Most silicates, as you point out, are not ionized and so will not show up on TDS readings. In fact, any un-ionized species in the water will not show up on TDS. A TDS meter is really nothing more than a conductivity meter. Only charged or highly polar species will cause electrical conduction so any neutral or non-polor species are invisible. There are many of such in water that could make it through a RO/DI system. Other than silicates, many elemental metals or dirt (alumino-silicates) may be another large source. Also biological shells, diatoms, etc. Also, many small organics like soaps, pesticides, oils etc could make it through in small proportions. I'm sure there are others as well. However, all that being said, a TDS meter is the easiest way for us to detect impending failure of our RO-DI units at home.

Hope this helps...Collin
 

Curtswearing

Mantisfreak
Joined
Nov 20, 2003
Messages
2,203
Location
St. Louis, MO
Nikki, this seems a wells studied and accurate write up.
Great job yet again Nikki!!!

cwcross said:
In fact, any un-ionized species in the water will not show up on TDS. A TDS meter is really nothing more than a conductivity meter. Only charged or highly polar species will cause electrical conduction so any neutral or non-polor species are invisible.
Collin, that is an excellent description that is simple and straight to the point. For people who want to read more on TDS, <<<see this link>>>. (There are some very important TDS Meter maintenance tips on that link).
 

kylem

A piece of the Reef!
Joined
Mar 22, 2004
Messages
85
Location
Milton-Freewater
DI resin

Does anyone have a solution to recharge resin in the DI units? I seem to go through alot of it because I have a high level of nitrates in the well water.
 
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