CO2 Injection

[Steve #1]

I'd like to start a discussion on CO2 injection. It seems it is often quickly shot down whenever it is brought up here for a number of different reasons but the discussion never goes very far. I think I'm in a slightly different situation where it would normally be ridiculous for me to even consider it other than that I think I would have most of what I need to set it up sitting around the garage and I typically use less than 2 gallons of acid a year and would rather not have it sitting around.

First question, how is CO2 typically introduced in to the pool? Low pressure? Is a venture needed? How about carbonating at high pressure then adding the carbonated water to the pool?

 

[kadavis]

This is one method, not very cheap. Welcome to Poolsmith Technologies

 

[JoyfulNoise]

You would need a CO2 tank with a decent regulator capable of getting you around 50-80psi pressure on the low side. You would also need a solenoid valve to start/stop gas flow and a check valve rated for gas use. A Venturi is not needed as that is only used in a low pressure gas application. You'd also probably want some kind of high flow gas limiter like the kind found on gas water heaters to control the flow in case of a failed solenoid or regulator. Most commercial systems use a pH probe to automate the solenoid but if you don't want that complexity you could just tie the solenoid to a timer and add a specific amount of CO2 each day. You probably also want a gas flow meter capable of reading ~ 50 CFH (cubic feet per hour) so you can track dosage. 50CF of CO2 at 50psi pressure is a lot and would roughly drop your pH by -2 units (so 7.5 --> 5.5) subject to dissolution and outgassing rates. You'd probably be operating at a lower pressure and flow point but it's something you'd have to really experiment with.

You won't get away from muriatic acid use though. Even though CO2 injection itself does not raise TA, your chlorinating liquid and fill water does (and plaster surfaces if your pool is plaster). So, over longer periods of time, TA will increase and the only way to knock it down is with MA. This is a well know problem with aquariums and hydroponics, CO2 injection can control pH but TA can still rise.

I realize you're looking for answers and how-to's but, honestly speaking, CO2 injection makes no sense in your situation if your total acid use is two gallons per season. If it were 20 gallons per season than that's a different story. But if you want to add a setup to your pool, go for it, should be an interesting project.

 

[Steve #1]

I realize you're looking for answers and how-to's but, honestly speaking, CO2 injection makes no sense in your situation if your total acid use is two gallons per season. If it were 20 gallons per season than that's a different story. But if you want to add a setup to your pool, go for it, should be an interesting project.

I'm more curious about how its typically done, and if I do put something together it will be more for the sake of putting it together than anything else. I have a significant amount of beverage equipment on hand so cost shouldn't be much of an issue.

One reservation I've had regarding CO2 is that I could go from a very easy to maintain PH to one that takes some work due to the CO2 off gassing. Is this a reasonable assumption?

 

[Bama Rambler]

I have all the equipment as well and have considered it, but since I use about zero acid per year, I haven't.

As Matt said, you'll need a regulator, but I'd go for a pressure of about 20 psig. All you need is something above your return pressure. Most keg regulators are capable of about 0-60 psig.

You'll also need an injection fitting of some type. My thought was to use a stainless steel diffusion stone like this. Insert it into the return line near the pool. You'll have to make sure only to inject the CO₂ when the return is flowing.

Matt's idea of a high flow shutoff in case of a solenoid failure is a good idea. Parker makes such an animal the FS190. It comes in limits down to .4 SLPM at 30 psig. It's a little expensive, but may be worth it if you ever had a hose or solenoid fail.