Shock & Acid

[kylepoolstylin]

Just started opening pool season. We’re shocking pools and adding acid if pH is high. A coworker of mine is sometimes hesitant to add muriatic acid and liquid chlorine at the same time. He says the chlorine will kill the acid and basically waste it. From what I’ve read here, the way acid and chlorine interact together is a key chemical relationship. Am I misunderstanding something? Do you first need some chlorine level readings before introducing other chemicals, or is adding both of these together right after taking off the cover effective? Thanks.

 

[mknauss]

Where do people get these myths?
I would suggest adding acid first to adjust pH. This is because when you add liquid chlorine, temporarily, the pH will rise a little. But as the chlorine is expended eliminating organics or from UV impact, the pH drops. Not a lot. but some.

This can be done one after the other. Best not to add acid and chlorine at the exact same time in the same spot. It could create chlorine gas, which is not good. We suggest waiting 15 minutes between additions.

 

[kylepoolstylin]

Thank you

 

[rack04]

Another thing to consider is more Hypochlorous Acid (HOCl) is present when Chlorine reacts with water at lower pH. A higher pH will result in a greater percent of Hypochlorite Ion (OCl¯), which has a lower disinfection ability. In sanitizing water, HOCl is 80-100 times more effective as OCl¯.

 

[mknauss]

Another thing to consider is more Hypochlorous Acid (HOCl) is present when Chlorine reacts with water at lower pH. A higher pH will result in a greater percent of Hypochlorite Ion (OCl¯), which has a lower disinfection ability. In sanitizing water, HOCl is 80-100 times more effective as Hypochlorite Ion OCl¯.

If there is CYA in the pool water, that effect is not significant.

 

[rack04]

If there is CYA in the pool water, that effect is not significant.

Understood. My comment was more theoretical from a background in water/wastewater treatment.

 

[Newdude]

From what I’ve read here, the way acid and chlorine interact together is a key chemical relationship

Cyanuric acid and chlorine, yes.
FC/CYA Levels

That is different from chlorine and Muriatic acid.

You should never add chemicals within 15 mins of each other, while mixing, as best practice. Granular CYA is slow to dissolve so it's ok to add liquid chlorine to a different area while the granuals dissolve.

 

[kylepoolstylin]

Cyanuric acid and chlorine, yes.
FC/CYA Levels

That is different from chlorine and Muriatic acid.

You should never add chemicals within 15 mins of each other, while mixing, as best practice. Granular CYA is slow to dissolve so it's ok to add liquid chlorine to a different area while the granuals dissolve.

Thanks, I’ve definitely been getting the relationship between pH, muriatic acid, and CYA a bit confused. I’ll put some more effort into testing and thinking about CYA going forward.