TDS higher after DI than before?!

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chris_pull

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I've just replaced my DI resin for the first time and surprised that it's reading 8 TDS after the membrane but 11 post DI? Am I missing a step or have I not packed it tightly enough, perhaps?

I checked the position of the inline TDS meter, which is correct.
 
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T-J

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Change the batteries on your TDS meter?
Switch TDS meter probes and see if you get the same readings?
Could be that the resin isn't packed enough?

Finally, from Mr. @Randy Holmes-Farley in a similar thread: "You sure its a mixed bed and not just a cation or anion resin? Using either of those alone will also boost the conductivity as larger ions are replaced by either H+ or OH-, both of which are very conductive."
 

MnFish1

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I would wonder about whether the inline meter is reading correctly. Its hard to tell exactly what you mean (maybe you do have it set up incorrectly?) - on my RODI unit - there is a TDS measurement from the faucet - and another one for the water after its gone completely through the system (i.e. after its gone through RO and DI).
 

Randy Holmes-Farley

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I've just replaced my DI resin for the first time and surprised that it's reading 8 TDS after the membrane but 11 post DI? Am I missing a step or have I not packed it tightly enough, perhaps?

I checked the position of the inline TDS meter, which is correct.

You sure it is a mixed bed resin? Using just anion or cation resin will raise the TDS in the effluent.

Assuming that's not it, I'd let it run a bit and see if it drops.
 

T-J

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You sure it is a mixed bed resin? Using just anion or cation resin will raise the TDS in the effluent.

Assuming that's not it, I'd let it run a bit and see if it drops.
I literally quoted this from you a post above yours! lol
 
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chris_pull

chris_pull

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I would wonder about whether the inline meter is reading correctly. Its hard to tell exactly what you mean (maybe you do have it set up incorrectly?) - on my RODI unit - there is a TDS measurement from the faucet - and another one for the water after its gone completely through the system (i.e. after its gone through RO and DI).
Yes, so I have the "input" probe after my RO membranes so that I can measure and flush high TDS creep water before it enters the DI, to increase the longevity of my DI; then I put the output probe after the DI, like you have. I used to have the input after the faucet (before RO) but this hardly changes and measuring the TDS level that enters the DI seems more informative to prevent TDS creep.

Change the batteries on your TDS meter?
Switch TDS meter probes and see if you get the same readings?
Could be that the resin isn't packed enough?

Finally, from Mr. @Randy Holmes-Farley in a similar thread: "You sure its a mixed bed and not just a cation or anion resin? Using either of those alone will also boost the conductivity as larger ions are replaced by either H+ or OH-, both of which are very conductive."
Good idea! I'll try swapping them.

You sure it is a mixed bed resin? Using just anion or cation resin will raise the TDS in the effluent.

Assuming that's not it, I'd let it run a bit and see if it drops.
It's from one of the larger RO companies here in the UK and sold as "INDION MB-115 colour changing mixed bed ion exchange resin" and listed as suitable for marine, so I assume it's okay to use? I tried running for about 5 mins and no change, so now I am beginning to think it could be the meter, though that's fairly new.
 
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You sure it is a mixed bed resin? Using just anion or cation resin will raise the TDS in the effluent.

Assuming that's not it, I'd let it run a bit and see if it drops.

Found this on the website: "INDION MB-115 is a mixed bed ion exchange resin. It is a mixture of highly virgin raw materials, strong acid cation and strong base anion resins in 40:60 volume ratio"
 

MnFish1

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Aside from the possibility of the ion issue, or the meter - the other thing could be some contaminant in the resin or the resin wasn't properly mixed (so you got more of one than the other). Otherwise I don't see any way for it to be higher after than before. except meter error. There are hand-held TDS meters you can get - it might work to just test the 'clean' water with that - if its still 11 - you know something in your system is not 'right'. I guess another thought is that since its 2 sensors - it could be that there is a margin of error, i.e. 8 is the same as 11 except for test variability. Which would suggest (as you mentioned) - that perhaps your media wasn't packed/mixed well?
 

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Found this on the website: "INDION MB-115 is a mixed bed ion exchange resin. It is a mixture of highly virgin raw materials, strong acid cation and strong base anion resins in 40:60 volume ratio"

So if you got what you expected to get, it should not rise.

You can test it by putting some in RO/DI with a little table salt and check the pH. Mixed bed will be close to neutral (say, 5-8). Above that or below that likely means its not a mixed bed.
 
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I've just replaced my DI resin for the first time and surprised that it's reading 8 TDS after the membrane but 11 post DI? Am I missing a step or have I not packed it tightly enough, perhaps?

I checked the position of the inline TDS meter, which is correct.
Did you make sure to pack the resin nice and tight?
 

MnFish1

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I agree with something someone else said - it can take some time - once you change the resin to get correct readings. For example - I have mine set with an overflow - when the bucket reaches a certain level - it stops. When it restarts - it can take an hour or so - to get back to 0
 
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chris_pull

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Did you make sure to pack the resin nice and tight?
I thought this was the issues as it was a problem when I first set it up, but I really pushed it in there with a plunger and don't think channelling could have been the cause, though I was prepared to take it all out and pack it in again!

As I say, it's now producing zero TDS water but I am still a bit unsure about why it was reading so high initially.
 
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chris_pull

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I'd change the batteries. Just to be safe.
Good idea. I may invest in a pen as well so I have way to double check erroneous measurements. I also made the switch to colour changing resin now, so it's nice to have visual confirmation that I've not somehow burnt through my resin!
 
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