DIY PH measurement and CO2 Injection System- Project Summary

[setsailsoon]

Folks,

I've been really busy with fine tuning the pool recently. We're going on vacation for 18 days (record for us). We have pool automation set up to use esp32 DIY controls... not anywhere as pretty and configurable as the Raspberry Pi solution others on here are using but I just don't have the time to work on that solution for at least a few months. I hope to then restart the Node JS project that many have been so helpful with especially @Katodude, @MyAZPool, and the guy that wrote most of the code who is also a member here (can't remember his id). In the meantime, my esp32 solution was quick, functional, and dirt cheap. Now I need to figure out how to get pH reasonably controlled while we're gone. I know I could do this with acid injection and even just get a pool service to add about a gallon every 3 days but I'd like to avoid both of those options. At a gallon every 3 days, I will require 3.7 pounds of CO2 every three says or say 1.3 # per day. This calculation makes some simplifying assumptions like no loss from off gasing and one mole of CO2 is ultimately equivalent to on mole of HCL. I can get a 50 # cylinder and that should last an entire month at least. I'm assuming in this calculation I get 100% conversion to carbonic acid. So here's a couple questions for the experts:

• Is 100% conversion reasonable to assume? @JoyfulNoise @JamesW any comments/suggestions
• from you on this?
• Seems like I'd be better off injecting down stream of my swg so I don't have too low pH that might remove catalyst on my swg generator, pump seals etc.. That's the last thing in the flow at the equipment pad. Does this make sense to you?
• Control should be pretty simple is there anything I'm missing on the web page below?

It only took a couple hours to get the code written using ChatGPT. The web page is printed below. I've set up a vpn that came with my old Orbi mesh wifi and it works great for me to access over the internet so I can intervene if needed.

Chris

 

[Katodude]

Why not just drop your pH down to 7.2, then throw as many tabs as possible in a floater. Water is not too warm now they should last a little over a week. Then deal with the higher pH when you come back. Sounds like you are overthinking it.

BTW. I have a fully functioning controller working and ready for you when you get back.

 

[setsailsoon]

Why not just drop your pH down to 7.2, then throw as many tabs as possible in a floater. Water is not too warm now they should last a little over a week. Then deal with the higher pH when you come back. Sounds like you are overthinking it.

BTW. I have a fully functioning controller working and ready for you when you get back.

Yep, I could definitely be. I've got the materials to try it out so I'll do that and have your plan as a great fall back. SWG seems to be holding the FC well. Push comes to shove I'll do it the simple way. All I need is to buy some more acid.

Thanks! And looking forward to finally getting the RPi working!

Chris

 

[setsailsoon]

I was able get the co2 tank today and have it ready to try out tomorrow. In the process I figured out a way to mount the pH probe with easily available materials. Turns out most of the probes available fit into a standard 1/2" push to connect fitting. Only problem is these are really tubing fittings and have a small flange to limit how far the tubing penetrated. Drill the flange out carefully from the pipe side of the fitting so you don't damage the o-ring. Then measure and push the pH probe so it's about middle of the pipe. Seals perfectly. I have a proper probe compression fitting on order but it's gonna take a while to get here.

I hope this is helpful to anybody else installing a pH probe.

Chris

 

[setsailsoon]

I did a manual test yesterday and guess what? IT WORKS!!!! I know, it's not that big a deal but it's really an accomplishment for me. I tried to make this a simple as I could. As Andy has already observed I can make things pretty complicated without even trying. So I'm using choked flow in the 1/4" tubing to control flow. It only takes 25 psi differential to do that and I add about 3 #/min this way. This is about 2-3 times what I calculate as needed each day. Starting pH last night was 8.0 and I gave it a 1 minute squirt. This morning pH is right at 7.5! Should have the electronics installed by this weekend! Pretty cool, huh?

Chris

 

[Katodude]

And if does work out think about how much club soda you can make.

 

[JamesW]

Why are you targeting a pH of 7.4?

In-Ground spa routinely has pH well above 8 upon weekly visits - what might be happening?

Here are my measurements from my last visit... 8+ 190 TA 350 CH 0 CYA 3200 Salt/TDS Inground spa size is about 1400 gallons. I adjusted pH down to 7.2 and the alkalinity came down to 170. Customer has naturally high alkalinity in the water. Upon filling the spa a couple months ago, the...

www.troublefreepool.com

 

[JamesW]

Is 100% conversion reasonable to assume?

I will require 3.7 pounds of CO2 every three says or say 1.3 # per day.

Multiply the Henry's Law Constant by the pressure by x 44009 to get ppm of Carbon Dioxide.

0.035 x 1 atm x 44009 = 1,540 ppm or 1.540 grams per liter.

1.540 grams per liter = 0.012852 lb/gal (pounds per gallon).

1.3 lb can be dissolved in 101.15 gallons of water if the Carbon Dioxide is 100% at 1 atm of pressure.

Temperature (°F)	Temperature (°C)	Henry's Constant (mol/L·atm)
50	10.0	0.0521
55	12.8	0.0480
60	15.6	0.0442
65	18.3	0.0409
70	21.1	0.0378
75	23.9	0.0350
80	26.7	0.0325
85	29.4	0.0302
90	32.2	0.0281
95	35.0	0.0262
100	37.8	0.0244
105	40.6	0.0228
110	43.3	0.0213

_____________________________________________
pH: 7.4.

Carbonate Alkalinity: 60

Carbon Dioxide PPM: 4.70 ppm actual.

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_____________________________________________

CO2 PPM Calculator for Equilibrium.

Temperature (°F): 76

Temperature (°C): 24.4

CO2 PPM: 0.6408. Equilibrium amount at 76 degrees F.

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claude.site

_____________________________________________

3.67 lbs CO2 is equal to adding 1 gallon of acid as far as lowering the pH.

Edit: It depends on the final target pH. For a target pH of 7.8, you need 3.8 lbs CO2. For a target pH of 7.5, you need 3.9 lbs CO2. For a target pH of 7.0, you need 4.49 lbs CO2 to match the pH drop of one gallon of 31.45% muriatic acid.

For example, with a TA of 110, you need 26 oz acid to lower the pH from 7.8 to 7.5. That's equivalent to 0.79 lb or 12.68 oz (weight) CO2.

Also, that's at 100% of the carbon dioxide getting dissolved into the water.

If the injection process is not good, you might have low efficiency in transfer, which will cause you to use more.

 

[JamesW]

The efficiency of injection depends on several factors.

100% conversion is not likely.

As a rule of thumb, a pool will use approximately 1/4 of a pound of CO₂ per 10,000 gallons a day.

The actual amount could vary based on a few factors, but as a rule of thumb, this is accurate.

pH PURE™ CO2 Injection for pH Control - Swimming Pools

Stabilizes pH & Total alkalinity with virtually no chemicals. CO2 Injection for PH control in swimming pools.

www.clearwaterpoolsystems.com

https://www.clearwaterpoolsystems.com/wp-content/uploads/documents/manual-PH-50.pdf

 

[JamesW]

We’re here to answer your questions, call us at 480.570.5716

Frequently Asked Questions | Poolsmith Technologies

What makes CO2 better for managing pH? How does our organic system work? Poolsmith Technologies provides detailed answers about our organic pH control system.

poolsmith.com

Contact Us | Poolsmith Technologies

Poolsmith Technologies provides CO2-based pH systems for residential swimming pools. Email or call us today to find the ideal one for your needs and budget.

poolsmith.com

 

[JamesW]

1.3 lb can be dissolved in 101.15 gallons of water if the Carbon Dioxide is 100% at 1 atm of pressure.

If the flow is 20 gpm, that indicates that the fastest you should inject 1.3 lb is 5 minutes.

Slower is better to help improve the efficiency of the process.

Smaller bubbles have more surface area per volume of gas, so that affects how well the gas is absorbed.

(Surface Area) / (Volume) = (4πr²) / ((4/3)πr³) = 3/r .

A 1 mm diameter bubble has a surface area to volume ratio of 6.

A 2 mm diameter bubble has a surface area to volume ratio of 3.

A 3 mm diameter bubble has a surface area to volume ratio of 2.

A 4 mm diameter sphere surface area to volume ratio 1.5.

A 5 mm diameter sphere surface area to volume ratio 1.2.

A 6 mm diameter sphere surface area to volume ratio 1.0.

You can watch the returns as the gas is injected to see if any bubbles out of the return.

The amount lost depends on how much you are over the equilibrium level.

CO2 PPM: 0.6408. Equilibrium amount at 76 degrees F.

pH: 7.4. Carbonate Alkalinity: 60. Carbon Dioxide PPM: 4.70 ppm actual.

4.70/0.6408 = 7.335 times over the equilibrium amount.

 

[setsailsoon]

Why are you targeting a pH of 7.4?

In-Ground spa routinely has pH well above 8 upon weekly visits - what might be happening?

Here are my measurements from my last visit... 8+ 190 TA 350 CH 0 CYA 3200 Salt/TDS Inground spa size is about 1400 gallons. I adjusted pH down to 7.2 and the alkalinity came down to 170. Customer has naturally high alkalinity in the water. Upon filling the spa a couple months ago, the...

www.troublefreepool.com

That was just one of the many, many runs I did when testing the software. I plan to run it at 7.8. Will run initially by controlling number of pulses per day. I think it's only going to take 2-3 pulses at 5 seconds each. I'll be able to track pH as it trends and eventually implement automatic mode with some limits and alarms that send me an email or text.

 

[setsailsoon]

The efficiency of injection depends on several factors.

100% conversion is not likely.

As a rule of thumb, a pool will use approximately 1/4 of a pound of CO₂ per 10,000 gallons a day.

The actual amount could vary based on a few factors, but as a rule of thumb, this is accurate.

pH PURE™ CO2 Injection for pH Control - Swimming Pools

Stabilizes pH & Total alkalinity with virtually no chemicals. CO2 Injection for PH control in swimming pools.

www.clearwaterpoolsystems.com

View attachment 629049

https://www.clearwaterpoolsystems.com/wp-content/uploads/documents/manual-PH-50.pdf

Thanks. I'll have to do a little trial and error to see how much I use vs calculated.

 

[JamesW]

What happens with the TA?

Carbon Dioxide does not do anything to the TA.

To minimize the loss of CO2, keep the pH as high as possible and the TA as low as possible.

Review the other thread where there is a lot of information about carbon dioxide.

 

[setsailsoon]

Multiply the Henry's Law Constant by the pressure by x 44009 to get ppm of Carbon Dioxide.

0.035 x 1 atm x 44009 = 1,540 ppm or 1.540 grams per liter.

1.540 grams per liter = 0.012852 lb/gal (pounds per gallon).

1.3 lb can be dissolved in 101.15 gallons of water if the Carbon Dioxide is 100% at 1 atm of pressure.

Temperature (°F)	Temperature (°C)	Henry's Constant (mol/L·atm)
50	10.0	0.0521
55	12.8	0.0480
60	15.6	0.0442
65	18.3	0.0409
70	21.1	0.0378
75	23.9	0.0350
80	26.7	0.0325
85	29.4	0.0302
90	32.2	0.0281
95	35.0	0.0262
100	37.8	0.0244
105	40.6	0.0228
110	43.3	0.0213

_____________________________________________
pH: 7.4.

Carbonate Alkalinity: 60

Carbon Dioxide PPM: 4.70 ppm actual.

Claude Artifact

Try out Artifacts created by Claude users

claude.site

_____________________________________________

CO2 PPM Calculator for Equilibrium.

Temperature (°F): 76

Temperature (°C): 24.4

CO2 PPM: 0.6408. Equilibrium amount at 76 degrees F.

Claude Artifact

Try out Artifacts created by Claude users

claude.site

_____________________________________________

Thanks James, very helpful. I've barely got my arms around ChatGPT. Will try Claude next.

 

[JamesW]

Where is the CO2 injected?

Contact time can make a difference.

Higher water temps and aeration increase the loss of CO2.

 

[setsailsoon]

What happens with the TA?

Carbon Dioxide does not do anything to the TA.

To minimize the loss of CO2, keep the pH as high as possible and the TA as low as possible.

Review the other thread where there is a lot of information about carbon dioxide.

Thanks, and yes I've looked at the info. This definitely isn't for everybody.

 

[JamesW]

I've barely got my arms around ChatGPT. Will try Claude next.

I use the free versions.

Sometimes ChatGPT does better and sometimes Claude does better.

The paid versions are supposed to be a lot better.

 

[setsailsoon]

Where is the CO2 injected?

Contact time can make a difference.

Higher water temps and aeration increase the loss of CO2.

I inject a couple feet downstream from the swg cell. This gives me about 75' of pipe before the returns. I have about 25-30 seconds of contact time. Yes, definitely won't be adding when I'm running the heater.

 

[JamesW]

Watch the returns to see if any gas bubbles out.

If the cell is on, you will get hydrogen gas, so make sure the cell is off when checking for bubbles.

What is the flow rate of water and what is the injection rate of carbon dioxide?