CO2 & RODI

[awais98]

Im in the process of setting up a new system in the new house.
My current issue is the DI resin gets used up VERY fast.... fast like 4 brute cans of RODI and its done! like 100 gallons only.

Been reading, researching and it seems like CO2 may be a problem.
In theory it seems right. Im in San Antonio and we get our city water supply from underground aquifer waters. Which I belive will be like well water.... very hard and now a lot of co2 apparently.
Researched a lot and seems the best way would be to get the RO water degassed in a storage bin and then pump it through the di resin.

4 questions for the knowledgeable.

1: Just checked my CO2 in RO water ( before the DI resin ) using the ph, alk and it comes out between 5-7 PPM. ( A confounding factor could be, its usually hot here, but this morning it is cool...water may be cooler and CO2 may be higher today? )
Is that high enough for the di resin to be used up? How much DI is used to neutralize X amount of CO2?

2: If after the RO I get a TDS between 3-5 with this new membrane, can I install ANOTHER RO membrane in SERIES..... so that the first RO membranes product water that is 3-5 TDS is now the input water for the 2nd membrane and so now 99% clearance of 5, will be very near 0, tds will be 0.05....
Will that work INSTEAD of DI resin??? or is the DI resin removing something else that is important. The Co2 if any will be taken care of with the powerhead mixing the salt, or just sitting in the ATO.
It will solve a hell lot of problems.

3: If I decide to regenerate DI resin... and actually seperate cation and anion in different cannisters....does it doecrease efficacy?
I read some where that I could do 3 cans: 1st cation, 2nd anion and 3rd mixed for perfection....
That way atleast the first 2 cannisters will be easy to recharge relatively quickly without removing them from the cannisters.

4: The water storage tanks will be in the garage, where with the cars can get pretty hot... like 100-110 in summer with 2 cars in there....
Will it harm the air stone degassing process....as the air pump will be using the garage air..... basically asking that with the cars not running but just hot in there, does the garage have a lot more CO2?? I know dumb question, but will be important to address in the planning stages...

Thank you for reading!!

Awais

 

[TheEngineer]

Could be CO2. For me, I'd go through a DI canister in under 10 gallons though. How are you measuring TDS? What is it on the incoming side?

What's the pH of your source water?

 

[awais98]

Could be CO2. For me, I'd go through a DI canister in under 10 gallons though. How are you measuring TDS? What is it on the incoming side?

What's the pH of your source water?

Answer:
1: TDS is measured through online meter, also confirmed with a hand held TDS meter.
2:On the incoming side it varies 280-320 preRO
3: Ph of the tap water ( this is after the water Softner) is around 7.4. The water that goes into the rodi.

Any answers to my questions?
Thanks

 

[TheEngineer]

I doubt it is CO2. Your pH should be low, not high, from high CO2 levels. You could try bubbling the water and see if it is. Take some water and put it in a glass. Run an air stone in it outside for an hour, check the pH again. If it goes up, there's excess CO2.

 

[mcarroll]

Make sure your waste and product lines aren't crossed.

Looking at your San Antonio Water Quality Report (well, this older one since the new ones don't track alkalinity) looks like they give you water with a nice, even pH of 7.7 but with an alkalinity of around 200 to 300 ppm of alkalinity.

That seems (using this and this) to translate to a CO2 level around 10 ppm.

When the RO strips all that alkalinity out, does that leave you with up to 7-10 ppm of unbuffered CO2 in the water?

Just thinking out loud...that jives with your calculation on the pre-RO water. pH only has to drop by half a point for the amount of CO2 to be double though, so good to keep that in mind.

 

[awais98]

I doubt it is CO2. Your pH should be low, not high, from high CO2 levels. You could try bubbling the water and see if it is. Take some water and put it in a glass. Run an air stone in it outside for an hour, check the pH again. If it goes up, there's excess CO2.

That pH of 7.4 is after the water softner, wouldnt other stuff in there cause the ph to rise, despite there being co2?
Sorry if i sound dumb.
I will check the ph of thewater from the garden hosebib, its doesnt go throught the water softner.

 

[awais98]

Make sure your waste and product lines aren't crossed.

Looking at your San Antonio Water Quality Report (well, this older one since the new ones don't track alkalinity) looks like they give you water with a nice, even pH of 7.7 but with an alkalinity of around 200 to 300 ppm of alkalinity.

That seems (using this and this) to translate to a CO2 level around 10 ppm.

When the RO strips all that alkalinity out, does that leave you with up to 7-10 ppm of unbuffered CO2 in the water?

Just thinking out loud...that jives with your calculation on the pre-RO water. pH only has to drop by half a point for the amount of CO2 to be double though, so good to keep that in mind.

Thank you for your reply.
The TDS of the product water from RO ( preDI) varies between 3-5, so I am thinking my product line and waste line are not crossed. Am I thinking right or I am still missing something.

Post RO water, had a pH of 6.2, and with a ALk of 5ppm, CO2 would vary between 5-7.


Icecool has put me in doubt. The Ph of my tap water ( after the softner ) is abounr 7.4-7.6 and my RO water is 6.2. It that wihtin range if I have CO2? or the tap ph should also be low. Im thinking as the tap has a lot of alk to it: 300, shouldnt that buffer and bring the pH up and hence I see it up?
Am I thinking along the right side?

 

[TheEngineer]

I don't think a water softener does much for CO2, but I don't know. I use an acid neutralizer on my well. My water comes in at a pH of 6.4.

 

[awais98]

I don't think a water softener does much for CO2, but I don't know. I use an acid neutralizer on my well. My water comes in at a pH of 6.4.

Happy to report:

Water pH

RO pre oxygenated 6.2!! Alk 5,Co2:5.5
RO post oxygenation 8.5!!Alk 5,Co2:0 [emoji7]

Indoor faucet preO2: 7.5
Indoor faucet postO2: 8.6

Garden hose preO2: 7.5
Garden hose postO2: 8.6

Even if ph probe is off on calibration, the consistency of the above results tells me that degassing will solve the issue!!!
Excited

 

[TheEngineer]

Excellent! I have a thread on how I degas my water on here if you want some inspiration.

 

[awais98]

Excellent! I have a thread on how I degas my water on here if you want some inspiration.

Link it

 

[Rick.45cal]

Here's the link to his degassing chamber thread: https://www.reef2reef.com/threads/diy-co2-degassing-chamber-for-ro-di.212587/

Cool idea, I may have to try building one

 

[awais98]

Here's the link to his degassing chamber thread: https://www.reef2reef.com/threads/diy-co2-degassing-chamber-for-ro-di.212587/

Cool idea, I may have to try building one

Thanks!!
I had seen that thread in the past

So to improve on his design, simply have 3 storage canisters( mine is 75G). 1st for RO with degassing airstone and also a pump to them pump water to the di resin and from there to the 2nd storage canister and 3rd for salt mixing.
Gravity DI feed problem solved.

 

[drawman]

Glad to hear the degassing is working for you! On one of my RO units I have the same issue and I just have lived with the idea that I'm going to burn through DI resin. Are you just running a pump in a reservoir to degas then pumping through a DI cartridge?

To add to the topic I know you talked about doing 2 RO units inline and scraping the DI. DI resin will remove so things that the RO membrane can't so I wouldn't really recommend it (your TDS may be low but there are certain things that aren't getting removed).

 

[awais98]

Glad to hear the degassing is working for you! On one of my RO units I have the same issue and I just have lived with the idea that I'm going to burn through DI resin. Are you just running a pump in a reservoir to degas then pumping through a DI cartridge?

To add to the topic I know you talked about doing 2 RO units inline and scraping the DI. DI resin will remove so things that the RO membrane can't so I wouldn't really recommend it (your TDS may be low but there are certain things that aren't getting removed).

To degass you use an air pump With a stone
And in the same reservoir have a pump to send that water to the DI.