Bad muriatic acid? Added gallon still high ph.


Well-known member
Oct 12, 2009
I added a gallon of Muriatic acid and my pH is still reading 8.2 which means it is presumably higher.

The pool calculator only goes to 8.6. Does that mean that is as high as my pH could be? If so according to the calculator I shouldn't have had to add that much to go from 8.6 to 7.5.

My muriatic acid was a couple years old and I've read that it doesn't "expire" so what gives?

BTW my FC is 5 and my CYA is ~40.


Well-known member
Mar 7, 2016
Gilbert AZ
I've had really weak batches of Acid...maybe your PH was sky high + weak acid?

Just add more let it mix and retest....repeat until you are good.

Also make sure whatever your using to measure the PH is accurate...if using drops make sure they aren't expired.


Mar 17, 2017
Villa Park/California
Do you know what strength it is? I purchased several bottles from Home Depot before realizing it was only 14.5%. A gallon of that stuff barely dented my pH and TA when it was high. Now I buy the HASA stuff from a local pool store. I think it is 31.5% and a much better value.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
Your pH could be much higher than the tester is capable of reading. And pH is logarithmic. The jump from 8.0 to 9.0 pH is ten times larger than the jump from 7.0 to 8.0. Just keep dosing with Now as 8.2 and eventually you'll get a shift. Once you're below the limit of the testblock, things should behave.

A good doublecheck is to compare your readings with what Effects of Adding Chemicals (bottom of poolmath) says about TA reduction for a given amount of acid. The pH calculation will be so far off you should try to not even read it but the TA drop is usually right on.

And also, if that acid is marked anywhere as "low-fuming" or "Safe" it is watered down.


Well-known member
Oct 12, 2009
It was the full strength muriatic acid I can guarantee that. I haven't measured TA mainly because I know the well water I filled my pool with has high TA and I didn't want to waste the drops.

My assumption was that continuing to drop pH would naturally drop TA. Sounds like a trip to Lowes for a new gallon or two of muriatic acid is likely the answer:

Also I've used two different test kits to test so the reagent isn't bad. One is brand new.


TFP Expert
Mar 2, 2011
You need to enter the TA into the calculator for the calculator to calculate the correct amount of acid to use to lower the ph.

If you’re waiting 24 hours to retest, the pH might have gone back up due to the high TA.

When adding acid, make sure the pump is on and brush the pool after adding the acid.

Retest after about 30 minutes after thoroughly brushing the pool.

Also, until the TA is correct, you should be lowering the pH to 7.2 each time.


Well-known member
Oct 12, 2009
TAis 220. High as I suspected. Added acid to reduce pH to7.2. I'll test again later. I didn't have time to brush but will do that if I have to add more.Thanks.


Well-known member
Jun 16, 2011
Las Vegas, NV
Sorry for the thread revival, but I've had the same (bad batches of muriatic acid) experience over the last few months with Home Depot's HDX muriatic acid. I always buy the most recently manufactured acid at Home Depot and bought several boxes over the course of a couple of months. I've been adding chemicals to pools for more than a few years, so I definitely noticed a trend of the muriatic acid not taking down the pH as much as expected. And I've been using Home Depot's HDX muriatic acid for the last couple of years.
I finally went to Lowes and bought a few gallons of Crown 1 gallon muriatic acid - in the paint aisle; 20 baume (31.45%), not pool strength (which is 10 baume, which is what the HDX was supposed to be).

I added a bit less than half the Crown muriatic acid vs HDX and was able to lower the pH at a rate I expected.

Bottom line: if you're buying Home Depot's HDX muriatic acid, use caution. It appears that they've gotten some bad batches. I live in Las Vegas so it may just be isolated to this area, but if you've had disappointing results using HDX muriatic acid, add your location so that other users can be aware of this problem.
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