Co2 and copper pipe?

Coinman

Member
May 22, 2010
14
Hello, I have a Hayward sense and dispense system using co2 to lower ph in my swg pool with a pro logic controller. The question I have will co2 being injected into a PVC return that is connected to an existing 1/12" copper line underground, will the copper be damaged by the carbonic gas? Any help would be appreciated.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
[EDIT] (deleted comment that is no longer applicable to previous post) [END-EDIT]. Just as CO2 outgassing causes the pH to rise with no change in TA, injecting CO2 causes the pH to drop with no change in TA.

So injecting CO2 will lower the pH of the water (it forms carbonic acid which is acidic) and this can be damaging to copper pipes if the pH drop is substantial, which it very well might be if such injection is for a relatively short period of time so uses higher quantity of CO2. I wouldn't use copper in such a line unless the injection was going to be very slow so over an extended period of time.

If you know the amount of CO2 that will be injected per time, the flow rate of the water through the pipe, and some of the water parameters such as pH, TA and CYA, then I can calculate the expected drop in pH.
 

Coinman

Member
May 22, 2010
14
Thanks for the reply, I have the sensor set up so if the ph rises above 7.5 the solenoid valve opens to disspences c02 to lower the ph. Hayward says with swg the ph creeps up so the co2 will keep the ph under control. I still wonder about how the TA will be, if I still have to add muratic acid to control TA the co2 will be not worth the hassle. I got the sense and dispense, wireless remote and wireless base station thrown in a package deal through Hayward with the pro logic PS-PL8 and T15 swg. I hoped the carbonic acid would be so diluted it would not affect the copper.
 

Coinman

Member
May 22, 2010
14
One more question. Tomorrow i'm geting my tile bead blasted, so the water needs to go down about a foot, with my new swg system people are telling me pool water gets old and should be replaced about every three years, my calcium level is about 450 and my water is about 10 years old, Hayward says the calcium should be below 300 with the swg. Should I replace my pool water? I just added the salt about a week and a half ago and it's level is perfect, I allready bought 400 lbs. of salt and 15 lbs of. conditioner for the new water. I don't mind replacing the water if it's necessary. Thank you!
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
There is no need to replace pool water unless something specific is wrong.

CH around 450 isn't ideal but you can live with that fairly easily if you have to by lowering your TA to compensate. Lowering the water a foot and replacing that will cut the CH level a bit, probably to below 400, at which point you probably won't need to worry about it at all.