I am puzzled by my RO/DI unit

[rlman41299]

Hello fellow reefers. Hopefully someone from here who is very familiar with how ro/di works would be able to answer my question.
I have a spectrapure mega maxcap 5 stage manual fluah ro/di and added another canister of di resin post unit. If you are familiar with this unit, this one has 2 di resin canister after ro membrane.
Now my question is this. Unit comes with a 3 way tds meter connected as follows: Before membrane, After membrane and between DI canisters.
Now my tap tds is at 414ppm which is high and post membrane meter reads 7ppm which I believe is still around 98% rejection rate. Now this is the one that is puzzling me. Post membrane reads 7ppm. POst membrane meter is connected in between membrane and first DI cartridge.
now my 3rd meter is connected in between both DI cartridge and is reading 14ppm? I have tried everything from using new meter to replacing batteries and still the same reading. I assume that since water has passed the first DI cartridge that it is supposed to read lower than the reading post membrane which is 7ppm. No wonder I go through a lot of resin on my second DI cartridge.
Product water is at 0ppm since I added another DI cartridge after the spectrapure unit and both input and output meter reads 0ppm.
Now I am not using spectrapure DI cartridge but rather using BRS DI resin.
First DI cartridge is filled with cation resin, second DI cartridge is anion resin and third DI cartridge is mixed bed DI resin.
Hopefully someone can shed some light why my tds reads higher between the first and second DI resin.
Thanks

 

[Biglew11]

Cation will add positive hydrogen ions to remove anything with a positive charge. Anion will then remove anything with a negative charge by add negative hydrogen ions.
I have 4 sensors on my unit.
1 on the input.
1 between membrane and first di stage.
1 between the second (anion) and the 3rd (mixed).
And the last one at the output of the 3rd.
When the 3rd sensor starts to read 1ppm its usually the anion that is used up and I change it out.

 

[Biglew11]

Also try flushing the first di (anion) for a while.

 

[KWT]

I have a spectra pure 5 stage that I added a pre sediment filter so I could run 2 carbon cartridges. Also added a 2nd r/o membrane, and I have auto back flush for the membranes. My TDS is 700-750 pre membranes and 0 on out put, I have not made enough water yet to need a cartridge change. May add another TDS meter in the future. Not much help, just my setup.

 

[rlman41299]

Cation will add positive hydrogen ions to remove anything with a positive charge. Anion will then remove anything with a negative charge by add negative hydrogen ions.
I have 4 sensors on my unit.
1 on the input.
1 between membrane and first di stage.
1 between the second (anion) and the 3rd (mixed).
And the last one at the output of the 3rd.
When the 3rd sensor starts to read 1ppm its usually the anion that is used up and I change it out.

So what are your readings post membrane and between di canisters? Are they same as mine where in between Di canisters is higher than post membrane? If that is the case, would it be better to just refill all 3 DI canisters with mixed bed resin?
@Biglew11

 

[Garf]

So what are your readings post membrane and between di canisters? Are they same as mine where in between Di canisters is higher than post membrane? If that is the case, would it be better to just refill all 3 DI canisters with mixed bed resin?
@Biglew11

Using separated beds are just easier to regenerate. I regen my own. Mixed bed usually 40%Cation 60%Anion (but you would have to get your RO water properly tested to get a more accurate mix), will give excellent results. You can mix it up yourself after a good rinsing.

 

[rlman41299]

Using separated beds are just easier to regenerate. I regen my own. Mixed bed usually 40%Cation 60%Anion (but you would have to get your RO water properly tested to get a more accurate mix), will give excellent results. You can mix it up yourself after a good rinsing.

Is there a good write up on how to regenerate your own DI? Is it same regeneration process for both cation and anion resin?

 

[Garf]

Is there a good write up on how to regenerate your own DI? Is it same regeneration process for both cation and anion resin?

http://www.reefkeeping.com/issues/2008-09/nftt/index.php

I use 18%hydrochloric (cation) 18%sodium hydroxide (anion)

 

[rlman41299]

Oh man that is a long process.

 

[Biglew11]

So what are your readings post membrane and between di canisters? Are they same as mine where in between Di canisters is higher than post membrane? If that is the case, would it be better to just refill all 3 DI canisters with mixed bed resin?
@Biglew11

145 coming into the unit, Right after membrane is around 3ppm.