De-ionization resin depletion

[dbrewsky]

Hello,

This is more a confirmation than anything, but its been bugging me on when I should change out my DI resin.

I have color-changing DI resin from Bulk Reef Supply in a dual DI stage with a 3-way inline TDS meter installed. I have noticed that the DI resin color indicates its time to change on both DI stages but my TDS only averages 1-2ppm going in to the first DI and has never registered above 0 TDS after this first stage.

Should I be relying on the color changing media or the TDS readings to determine when the DI resin is spent???

I have been going by the TDS readings, just curious if I am missing anything.

 

[Randy Holmes-Farley Verified Community Expert]

I'd go by the TDS, assuming it does eventually rise and is not broken.

 

[PedroYoung]

I'd go by the TDS, assuming it does eventually rise and is not broken.

I actually ran mine with DI resin removed to confirm the TDS meter was working.

 

[dbrewsky]

ok, I know that the first stage meter does report TDS readings. Is the color change something to be concerned about if I can confirm that the other inline meters are functioning?

 

[AZDesertRat]

You need to be monitoring 4 TDS readings to troubleshoot your dual DI system. Tap water TDS, RO only TDS before the first DI, first DI TDS and final RO/DI TDS.
The first two tell you how well your RO membrane is performing and are used to calculate the membrane rejection rate or removal efficiency. The first DI tells you when that cartridge is exhausted at which point if you ae using the same resin blend in both cartridges you would remove the exhausted first DI and move the second cartridge into the first position. Repack the exhausted DI and install it in the second position.

The best thing you can do is forget you even own the inline TDS meters and buy a good ATC temperature compensated handheld TDS meter which is much more accurate and can be used anywhere since it is not dedicated. About $25-$30 a HM Digital TDS-3, TDS-4TM or AP-1 and any are a much better choice than the inlines.

If you like the inlines for some reason, you need two dual inline meters to accomplish what you need. The left hand meter would read the tap water with the IN probe and the RO only with the OUT probe. The right hand meter would read the first DI with the IN probe and the finished water what the heck the OUT probe. I have two dual inlines but let the batteries years ago since I only rely on the handhelds for accuracy reasons.

 

[dbrewsky]

@AZDesertRat - thanks for the input! I have been meaning to pick up a handheld TDS, so I will definitely pick one up for spot testing water samples.

I did want to clarify that my in line meter is average 1-2TDS after the RO membrane. The reading after the first DI stage is 0TDS and after the 2nd DI state is 0TDS as well. The curious thing is the color change resin in both stages is the same shade of orange through out which visually would indicate that it is being used up.

Ill post back once I get some handheld TDS readings to compare.

 

[AZDesertRat]

Color changing resins can be very inaccurate. It can change in streaks, top to bottom, bottom to top, all at once, never or whatever. Don't waste your money on color changing resin, stick with good non color changing and always use a handheld TDS meter that is ATC compensated.

 

[dbrewsky]

ok thank you, I appreciate your insight and will monitor TDS when determining DI depletion.

 

[Zoot098]

I rely on TDS inline and a handheld TDS
My resin seems to turn from blue to brown after only 70 gallons or so

 

[dbrewsky]

@Zoot098 - glad to hear others are noticing this as well!

 

[Zoot098]

@Zoot098 - glad to hear others are noticing this as well!

I think the color change is designed so you buy more LOL

 

[Randy Holmes-Farley Verified Community Expert]

I do not have concerns with inline meters the way AZDesertRat does.

 

[AZDesertRat]

The biggest issues with inlines is they do not sense water temperature like ATC handhelds do so can be significantly off in their readings and they cannot be calibrated. If you have ever cut an inline probe apart you would find it has a temperature sensor but it is inside the fat portion behind the little rectangular window so measures air temperature which is rarely the same as the water temperature from the tap. This is a big built in error you cannot fix.

With the ATC handhelds you immerse the temperature probe in the liquid so much more accurate. You can also calibrate the ATC handhelds. I like low end accuracy when it comes to RO and DI so for me an inline is more like a litmus paper test, kind of like you have TDS or you don't but you really have no accurate idea how much.

 

[Randy Holmes-Farley Verified Community Expert]

I don't see a reason to think that is an issue. So what if the conductivity is reading high or low by a substatntial factor? 2x? 4x? It never changes the zero point, so anything above 0 ppm TDS is time to change the resin. Both inline and handheld can make that decision.