RO/DI cation not being consumed?

[AaronFReef]

I have a self-assembled 7 stage RO/DI with 3 stages of DI in the BRS fashion with cation->anion->mixed bed (cation color changing).

Note that in this picture the RO membranes were running serially but due to my hard well water I am now running them parallel since the average TDS they pushed out was fairly high and I’m running through DI too fast. In other words the waste of one used to go to the inlet of the other but now they both are fed from the prefilters.

So anyways, my anion resin runs out after about 75 gallons with 20 TDS RO as input and they output 0 TDS. I imagine this could be due to the CO2 levels in my well water but I’m not willing to do an aeration chamber and then booster pump setup.

I’ve now run about 250 gallons of RODI through these and I see no sign of color change on my cation or mixed bed resins. The TDS says zero but I’m concerned that something isn’t right with zero discernible color change. I even replaced the mixed bed (which was originally anion color changing) to the cation color changing resin and neither have shown ANY sign of color change. What could be causing this? Should I be concerned?

Edit: I do flush my RO membranes every time I turn this on or off and don’t feed RO into the DI until it stops at 20 TDS.

 

[KJoFan]

Following this as I have a similar situation. I run the 3 stage DI with cation as first DI stage, I have not changed it since I set it up several months ago. Anion however, I change after about 200g of finished product. Mixed bed is changed maybe every other time I change the anion stage.

My guess is the high CO2 chews through the anion. I'm unsure what the cation stage is meant to remove (I know I read it once but have since forgotten), but I can only assume whatever it is, my water out of my RO doesn't contain much of it. My TDS out of my RO is a bit lower than yours but even so.

 

[AaronFReef]

Following this as I have a similar situation. I run the 3 stage DI with cation as first DI stage, I have not changed it since I set it up several months ago. Anion however, I change after about 200g of finished product. Mixed bed is changed maybe every other time I change the anion stage.

My guess is the high CO2 chews through the anion. I'm unsure what the cation stage is meant to remove (I know I read it once but have since forgotten), but I can only assume whatever it is, my water out of my RO doesn't contain much of it. My TDS out of my RO is a bit lower than yours but even so.

I feel like I’ve read that it absorbs positive ions, so that would include iron (Fe+) and copper and lots of metals which are cations.

 

[KJoFan]

I feel like I’ve read that it absorbs positive ions, so that would include iron (Fe+) and copper and lots of metals which are cations.

Yeah that sounds right, now that you say it. Which, I know for me my water contains those things, especially iron. But, I also am running my source water through a water softener first which should remove a lot of those impurities already, so maybe that's why it goes easier on the cation resin.

Like you though, I don't want to, nor have room to aerate my water before pumping it through the RO/DI unit.

 

[AaronFReef]

But a water softener should add potassium which is a cation and need to be removed. I think water softeners just exchange one impurity for a more desirable impurity.

 

[ca1ore]

I feel like I’ve read that it absorbs positive ions, so that would include iron (Fe+) and copper and lots of metals which are cations.

That is exactly what is happening. I also use the three DI cannister setup. Anion resin lasts me about 500 gallons. Cation and Mixed bed last for thousands of gallons. That's the whole point of going with the three different types.

 

[ca1ore]

But a water softener should add potassium which is a cation and need to be removed. I think water softeners just exchange one impurity for a more desirable impurity.

Sodium usually; though you can use potassium salt as well in a home water softener. Most of the sodium gets taken out by the RO membrane.

 

[KJoFan]

That is exactly what is happening. I also use the three DI cannister setup. Anion resin lasts me about 300 gallons. Cation and Mixed bed last for thousands of gallons. That's the whole point of going with the three different types.

I'm not sure it's ended up cheaper in the long run though, do you think? I used to change mixed bed at the same frequency I'm changing anion, so did I end up really saving anything? I'm not sure.

 

[ca1ore]

It certainly has been cheaper for me. It is odd that you are burning though the anion so fast though. I'm getting 5-6x more out of mine than you are (my prior post should have said 500 not 300); and I'm on a well too.

 

[AaronFReef]

Thanks ca1ore. I only get about 60 gallons I’d guess. Perhaps very high CO2. It’s an ancient deep aquifer I’m pulling from.

 

[KJoFan]

It certainly has been cheaper for me. It is odd that you are burning though the anion so fast though. I'm getting 5-6x more out of mine than you are (my prior post should have said 500 not 300); and I'm on a well too.

I think it's probably a CO2 issue for me too, though I haven't confirmed it. I may get more than 200g of final water out of a canister of anion. I just changed mine last weekend and made probably 175-200g of water throughout the course of the weekend. I should look at the canister and see how much has changed color. Maybe I could squeeze a bit more out of it but I tend to change it when the entire canister has changed color in order to preserve my mixed bed a bit more.

 

[KJoFan]

I looked at my canister this evening and with my estimated 175-200g of finished water, half of the anion canister has turned yellow. So...maybe I'll get around 400g out of one canister. I'll have to see for sure. Maybe it's not as bad as I thought initially.

 

[JMetaxas]

I eat Anion resin in about 200 gallons.( I have high CO2 in my well water) My cation resin seems to last forever. Best thing I ever did was use dedicated resin beds. Mixed bed resin was getting eaten up way too fast.

 

[AaronFReef]

I eat Anion resin in about 200 gallons.( I have high CO2 in my well water) My cation resin seems to last forever. Best thing I ever did was use dedicated resin beds. Mixed bed resin was getting eaten up way too fast.

Glad to hear it was worthwhile. I only get about 60 gallons. You guys are lucky.