Poolsmith CO2 injection for pH control

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,620
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
It would be nice if you could do a cost comparison versus MA based on your best local prices for both products. It’s good info to have documented here so other in different regions can compare. Sounds like the system is working out great for you and it seems fairly simple enough to work with.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
The best local price for CO2 refills I have found is $25 for a 20 lb tank. For my pool, that translates to a yearly cost of about $175 for CO2. At my previous acid demand rate, I needed about 25 gallons of acid each year at about $6/gallon, about $150. So pH control using CO2 is slightly more expensive for me, but not enough to make any real difference. However the initial investment in the CO2 equipment is pretty high (about $1600 all in for the complete system with three empty tanks). So it's a tradeoff between cost and convenience. Personally, I'd rather refill the tanks every four to five months than have to add acid every three or four days. The alternative would have been to install an automatic acid dispenser, and I just couldn't get comfortable with that solution.
 
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red-beard

Gold Supporter
May 27, 2019
1,395
Houston, TX
Pool Size
25000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite Pro (T-15)
How is your fill water? I just did a lot of work to reduce my Carbonate alkalinity to 30-40. I did this by adding borates to 50 ppm and then lowering TA, while running an 80 ppm CYA.
My pH is now VERY stable. I'm adding maybe 2 quarts of MA per month.
 

jseyfert3

Silver Supporter
Bronze Supporter
TFP Guide
Oct 20, 2017
1,857
Southern WI
Pool Size
15000
Surface
Vinyl
Chlorine
Liquid Chlorine
Don't think it's a temperature thing. It had been consistently right around 500, then started to drop over the course of a few days and hit zero about three days ago. I guess the scale is large enough that low pressures don't register.
This sounds like your pressure gauge isn’t reading right. At room temps tanks that have liquid CO2 are about 850 psi. They don’t reach 500 psi until they are just above freezing. Outdoors, higher than room temp, the pressure would be even more than 850 psi. https://www.agas.com/media/2426/r744-pt-chart.pdf

For example, the gauge on the CO2 regulator of my preferred type of CO2 injection, that of homemade beer, the tank for which lives inside my homemade kegerator at approximately 39 °F.
full


full


Before it lived inside, at room temp it was 850-900 or so, and on hot days it was definitely on the higher side of that.

An offset doesn’t matter much, since the pressure only varies by temp until the liquid is exhausted, at which point it starts dropping and the tank is nearly empty. The offset explains why you continued getting flow for a few days after your gauge read zero though.
 
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cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Switched over to the third tank this morning, so adjusting for the time the system was off-line, the second tank last just over 7 weeks. So I expect I'll be needing to refill the tanks around labor day, which would be right around five months since I first turned the system on. So far, so good.
 
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cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
A point worth mentioning about the Poolsmith controller, it has some idea of elapsed time (so for example it knows when approximately 24 hours have passed since the start of the last injection cycle), but it doesn't have a clock (so no concept of date and time). This is relevant because if you lose power (like we did for a couple hours yesterday) or if you turn the controller off, when power is restored the elapsed time counter starts all over again and it will immediately begin a new set of injection cycles. It does have a pressure sensor so it knows if the pump is running, so presumably if power is restored while your pump happens to be off, it won't start counting the injection cycle time until the pump starts again. Haven't tested that out myself since I run my pump continuously, but I'm pretty sure that's how it works. So basically, you can't set a schedule for injection, and you might get an extra injection cycle on a day when power is lost, but you shouldn't get into a state where it is not injecting periodically as long as power gets restored at some point.
 
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Rattus Suffocatus

Silver Supporter
Jun 5, 2019
1,447
Corona de Tucson, AZ
CO2 is crazy non-linear over temperature. It is just a bizarre gas to work with-- it can be completely stable at the triple point-- literally at all three phases (not plasma, obviously) at once. So, yeah a high pressure gauge on a tank is really only a good indication if you still have liquid at the bottom. You can't really read anything else into it. I'd almost be nervous about leaving a tank out in the sun here in Tucson.. but the tanks are rated for that....

And honestly.. doing CO2 for beer for several years in both Cedar Rapids, IA and Tucson, AZ, by far the consistently best place to get CO2 isn't from a welding gas company-- it's from the fire extinguisher companies... even if it's a dollar or two more for a 20# tank refill the service is 100x better from the fire extinguisher companies. 2/2 in two places versus 0/2 with "airgas"....

For beer my 10# tank lasts me about 3 years... I guess I don't drink much... but next time I'll have to spring for a hydrotest.... so yeah.. the tank expires before I get the second refill....

I like that Kegco low pressure gauge... It actually lists "lambics"! :)
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
Around here, the only places I've found that will do refills are fire safety companies. Welding supplies will only do tank exchanges. The cheapest refill price I've found is $45/tank (20 lb. tank). Cheapest exchange is $25 (most are higher). I did a refill because I have nice new tanks and I just couldn't bring myself to trade them in.
 

red-beard

Gold Supporter
May 27, 2019
1,395
Houston, TX
Pool Size
25000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite Pro (T-15)
I need to do an exchange, since all of my tanks have expired...

Just like my propane tanks...too old? Go to Blue Rhino...
 

Rattus Suffocatus

Silver Supporter
Jun 5, 2019
1,447
Corona de Tucson, AZ
Yeah.. never buy a new tank. Buy your initial one from an "exchange". You won't get attached to it that way. But I guess I am lucky in that the fire extinguisher places I used were only like $5 more than the welding shops, and in both cases they use "food grade" CO2 for both the extinguishers and the carbonation tanks. I suppose for a pool that doesn't matter, but it's nice for beer and soda.

Next time I will need to spring out another $25 for a hydrotest though... so I guess overall it might be a little more expensive.
 

cptkirk

Well-known member
Jul 29, 2018
208
FL Panhandle
In my area, buying a full tank without an exchange from Airgas was not much different in price than buying a new tank and getting it filled at the fire safety place, and Airgas's exchange price was about the same as the refill price. I didn't find the cheaper exchange price at another place in another town until afterwards. Oh well.
 
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