Can muriatic acid go inert?

[geh]

I have a curious issue with my pH and muriatic acid. While I was out of town for two weeks my wife was handing the pool chemistry for me (her first time). She was using the Taylor test kit and the pool math app. At one point the pH was 8.0, and when she would add muriatic acid she would get the same result the next day.

When I got home yesterday I performed the chemistry tests, pH was 8.0, and the acid demand tests indicated 4 drops to lower the pH to 7.6. I added the correct amount of muriatic acid, 1 qt. 24 oz., from a case I had bought right before I left town (the same one my wife had been using).

Later tests that evening and again this morning, showed zero change in my pH level. The test acid demand test was again showing 4 drops to reach 7.6 pH.

I will add she left the acid outside where it was exposed to afternoon sun, but also the glue from the jug seal was black and bits of it were crumbling into the measuring cup. I also know my local pool store's warehouse is not climate controlled and it gets very hot from the New Orleans summer. Is it possible the sunlight exposure or the warehouse storage could have neutralized the acid? Adding a few photos from my phone after I post this.

Thanks/g

 

[mknauss]

Acid is not bothered by storage conditions, other than the plastic jug can get compromised after a very long time in the sun.

Check that the acid you purchased was the same strength of what you have used in the past.

 

[geh]

Yes, it is the 31.45% that I have always used, but a different brand

 

[Toxophilite]

All pools not being equal, and someone with more pool chemistry knowledge might have your answer, but looking at your pool logs your pH has run consistently high and with some high doses of MA prior added. Our pools are near equal volume, and I have to add 28oz every third day. That takes me from 8.0 to 7.6 without fail. You seem to be adding much greater amounts of MA and getting very little pH lowering, and not a new issue.

 

[mknauss]

If it is clearly marked at that %, it should be that %.

 

[ajw22]

Reviewing your PM logs I see when your TA is 70 your pH is in the mid 7's. When your TA is 100 your pH likes to be about 8.

Your higher TA and your SWG together are driving your pH higher.

Lower your TA to 60-70 and your pH should settle in the 7.6-7.8 range.

 

[geh]

update: not sure why, but now I have a pH reduction. Strange how two tests in a row indicated no change. Not sure why it was responding to the acid demand test but not to the acid.

 

[geh]

Reviewing your PM logs I see when your TA is 70 your pH is in the mid 7's. When your TA is 100 your pH likes to be about 8.

Your higher TA and your SWG together are driving your pH higher.

Lower your TA to 60-70 and your pH should settle in the 7.6-7.8 range.

Thanks, that is a great observation. Yes, just got back home and plan on balancing everything over the next two days. My CYA also dropped due to heavy rains and backwashing.