CO2 vs Muriatic Acid

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Pool Gec

CO2 vs Muriatic Acid

Postby Pool Gec » Mon 08 Jan, 2018 12:04

CO2 vs. Muriatic Acid : Question Assuming a balanced pool, how much CO2 would be used to manage pH verses the same pool using muriatic acid


Teapot
Pool Industry Leader
Pool Industry Leader
Posts: 1337
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: CO2 vs Muriatic Acid

Postby Teapot » Mon 08 Jan, 2018 12:52

Impossible to answer, depends on temperature, bather load, alkalinity of water supply and how many splashing swimmers/children in the pool. Only thing I can say is unless you have access to a low/no cost source of C02 it's going to be expensive possibly x2
Pool Gec

Re: CO2 vs Muriatic Acid

Postby Pool Gec » Thu 11 Jan, 2018 13:36

Teapot,

I understand that changing variable don't allow an accurate measurement of how much acid vs CO2 would you use on a specific pool. What I am asking is the cost relationship between the two options. I take it from your comment that you believe that acid is cheaper to use vs. CO2. What cost of acid do you base your projection of increased cost of x 2? Do you have any experience using CO2 vs Acid in a commercial pool setting?

Is there anyone on this blog that has some real experience with CO2? Is so please respond.
Teapot
Pool Industry Leader
Pool Industry Leader
Posts: 1337
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: CO2 vs Muriatic Acid

Postby Teapot » Thu 11 Jan, 2018 15:40

To be fair Pool Gec, there is a lot depending on it. The only pool I have worked on that used CO2 was a small hotel. Being small they didn't buy in bulk so were paying more for everything. don't forget the cost of delivery and servicing of the gas equipment compared to a peristaltic pipe change.

There is a lot dependent on the water in the pool and the top up water as to how much you'll use but CO2 is a weak acid and at pool pH a fair amount of the CO2 will be adding to the carbonates in the water increasing the alkalinity further and creating a bigger pH buffer. So you'll most likely use more as muratic acid to fight that as muratic lowers alkalinity as well it's difficult to compare, Many pools can benefit from a lower alkalinity (slows the pH rise) and a small compensation by increasing the pH (pH produces the biggest change in LSI)
If you could obtain costs for each muratic and CO2 and some idea of the water chemistry we'd be in a better place to judge.

On a commercial pool with commercial sized storage the difference maybe smaller say 1.25-1.5x more with CO2. I would be interested to know the answer on this as well bearing in mind different country and several years ago.

Sorry I haven't written that very clearly, if you haven't understood I'll try again.
Oojsh
I'm new here
I'm new here
Posts: 3
Joined: Sat 10 Apr, 2021 19:21
My Pool: 50kL, Zodiac Tri SWG, fiberglass, 1kW pump, cartridge

Re: CO2 vs Muriatic Acid

Postby Oojsh » Sat 10 Apr, 2021 20:09

Have had DIY CO2 injection system running for approx. 2 months - still early days but details so far:

55kL pool w SWG previously using 500-800ml acid per week (Summer).

CO2 system has gas flow rate set at 1 LPM, on duty cycle of 4% (1min on, 24mins off) and is active while pump is running (7 and now 6hrs/day)

pH previously used to rise close to 8.0 each week, now CO2 system keeps constant at 7.4-7.5 - if nothing else, the more consistent pH should result in more effective chlorination more often as effectiveness is significantly reduced in the high 7's pH range.

The first 6kg bottle of CO2 (AUD66) only lasted 2 weeks, however this was before getting flow/duty dialled in (at one point I ran from pH8.0 to pH7.0 in 3 days consuming way too much gas) and may also have had small system leak. The refilled tank has been running 6 weeks and pressure still reads at CO2 liquification pressure (~7000kPa).

If the tank lasts for 10 weeks, I calculate this system will be about 3x more expensive than acid - however, for the reduced effort of manually adding Acid (ugh), and benefit of improved chlorine effectiveness, I'm happy with that.

Will report back here next time cylinder runs empty.
Teapot
Pool Industry Leader
Pool Industry Leader
Posts: 1337
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: CO2 vs Muriatic Acid

Postby Teapot » Sun 11 Apr, 2021 07:13

Thats good up to date info for your location. As I said before and frequently on here, lowering the TA will dramatically reduce the pH rise. Also there is no problem running with a pH of 8 if you are using CYA stabiliser in the water as there is negligible effect on chlorine efficiency. The most important factor is sufficient free chlorine to CYA ratio.
Oojsh
I'm new here
I'm new here
Posts: 3
Joined: Sat 10 Apr, 2021 19:21
My Pool: 50kL, Zodiac Tri SWG, fiberglass, 1kW pump, cartridge

Re: CO2 vs Muriatic Acid

Postby Oojsh » Sun 11 Apr, 2021 17:19

Hi Teapot
Have seen the recommendation to run low TA (to reduce rate of CO2 offgassing) and allow high pH (to offset and maintain near zero LSI) quite a few times across forums (by experienced posters), but haven't seen links to studies corroborating that chlorine effectiveness will be maintained at those higher pH values - ie. evidence that free chlorine present as hypochlorite ion
is just as/or more effective a biocide compared with free chlorine present as hypochlorous acid.

So far my research indicates otherwise - but may be missing something / more recent results.

Best quick summary I can find:
https://www.pwtag.org/importance-of-fre ... tent-tn60/

Best referenced scientific article I can find:
https://www.ncbi.nlm.nih.gov/books/NBK234590/
Sections:
> Chemistry of Chlorine in Water
> Efficacy against Bacteria - Free Chlorine (HOCl and OCl-)
Teapot
Pool Industry Leader
Pool Industry Leader
Posts: 1337
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: CO2 vs Muriatic Acid

Postby Teapot » Mon 12 Apr, 2021 10:50

Ok yes you are correct with your research but that is for chlorinated water in the absence of CYA which has a dominant effect of efficacy of chlorine. I have a paper which tests this and documents the effectiveness. I posted it on this website but cannot locate it. If I can post it or a link to it I will.
BTW, PWTAG talk mostly bollocks! Never have I encountered such people and have many "discussions" with them over the fundamental lack of understanding of actual pool water chemistry. They prefer to hold on to old incorrect information and continue to publish it to defend the industry possibly.
Oojsh
I'm new here
I'm new here
Posts: 3
Joined: Sat 10 Apr, 2021 19:21
My Pool: 50kL, Zodiac Tri SWG, fiberglass, 1kW pump, cartridge

Re: CO2 vs Muriatic Acid

Postby Oojsh » Tue 13 Apr, 2021 06:23

found what i suspect may be the paper referred to:

Stanley R. Pickens - Relative Effects of pH and Cyanurate on Disinfection
https://cdn2.hubspot.net/hubfs/3831534/ ... ickens.pdf

Also very interesting related info here:
Richard Falk - The Chlorine/Cyanuric Acid Relationship and Implications for Nitrogen Trichloride
https://cdn2.hubspot.net/hubfs/3831534/Chlorine-CYA.pdf
also Richard
https://www.troublefreepool.com/threads ... istry.558/

and above fairly well summarised by OrendaTech here:
Chlorine, pH and Cyanuric Acid Relationships
https://blog.orendatech.com/chlorine-ph ... ationships

Additional
The Effect of Cyanuric Acid on Disinfection
https://www.pulsarsystems.net/uploads/7 ... ection.pdf


Still more reading to do, but, went in a skeptic and coming out a convert!
Will likely increase target pH to 7.8 at least and drop TA accordingly.
Teapot
Pool Industry Leader
Pool Industry Leader
Posts: 1337
Joined: Tue 17 Oct, 2017 10:52
My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: CO2 vs Muriatic Acid

Postby Teapot » Tue 13 Apr, 2021 11:11

My work is done!

With thanks to Richard Falk for his help over the years.

Return to “pH & Total Alkalinity”

Who is online at the Pool Help Forum

Users browsing this forum: Applebot [Bot] and 5 guests