Poolsmith CO2 injection for pH control

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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.
 
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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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.
 
cptkirk said:
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.
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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


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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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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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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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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"! :)
 
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.
 
I need to do an exchange, since all of my tanks have expired...

Just like my propane tanks...too old? Go to Blue Rhino...
 
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.
 
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.
 
JoyfulNoise said:
I haven’t looked around my area fir pricing but I wouldn’t be surprised if it were as expensive. Welding supply shops are probably the cheapest source but you usually have to buy big tanks. Hopefully you can get a lot of use out of those three tanks before you need to exchange.

If you control your aeration sources and keep the pool covered, you won’t use much CO2. pH control is all about outgassing of CO2. The better you control that, the less fiddling with pH is required.
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CO2 system Just so you know … 26 years of rental spa …

We have 9 spas on chemtrol 250’s with 4 tanks online always … 2 on live…. 2 ready on a auto switcher. We do get our CO2 from a welding supply.

we use the tall tanks we paid For them and we have no $6.00 monthly rental.
Its $125.00 for like 6 delivered.

The Co2 lines are Pex at around 40-70lb and we buy 110v Solenoids on eBay (watch the model for diameter and volume) for $20.00 about …

we mount that to a bell box
with a pex shut off at each tub…

we have a inline adjustable air flow meter on each tub. (Like for oxygen)
And small 1/8“ Black poly tube output at each spa (with needle valve).for adjustments after the Soloniod.

We use Injectors made by the pump people (for Dolphin 10) (sorry forgot name) that is 1/2” inline back to the spa.

We use liquids chlorine and Blue-White $34.00 chlorine Injectors… from carboys of chlorine.

The Co2 lasts us 2 weeks about ..

and we over shoot both ways since we are stupid..

what is key is no leaks… Pex is Best.. for us… we also use backflow on multible locations. And shut offs around the line… make surte if you do many rooms enter in middle or make a loop. So they feed right.

use the valve On the Pex to cut 1/2 the presure out… but. We learned that Asco makes a few more then 3,000 styles… and one can open 20x more Then the bomb proof units (or some nonsense) it will be best to use same models …

good luck …
 

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