Chemistry confusion!

[Flboy44]

As I’m retraining myself on pool chemistry, I am trying to deal with what seems like contradictory information!
As a SWG system, I understand the continuing need for muriatic acid for PH balance. But I didn’t think this would also affect TA so much!
I really was under the misconception of certain set it and forget it chemicals! Being, salt, calcium, CYA, and TA! Of course water loss and major rain does screw with this!
I added two cups of muriatic acid for high PH, and my TA went from 75 to 39! Now, I didn’t do an acid demand test and just guessed!
I definitely overshot the muriatic, PH went to 7.1! Was approx 8.0.
Is this the cause of the TA dive? Or just normal chemistry and joy of pool management?
I guess, in much fewer words, is TA a measurement that has to always be tweaked?

footnote, really am working on reducing explanation points!!

 

[mknauss]

Something does not add up. 16 oz of 31.45% muriatic acid in 12000 gallons of water would reduce pH by 0.3 and lower TA by 5

 

[MITBeta]

Where did you get those TA numbers? Those didn't come from your Taylor test kit.

 

[Flboy44]

Something does not add up. 16 oz of 31.45% muriatic acid in 12000 gallons of water would reduce pH by 0.3 and lower TA by 5

You are correct! Hate to admit it, but part of what happened was a really careless add of muriatic acid! It was a damaged bottle that I was trying to use up and I’m fairly sure I added at least a quart! Didn’t do an acid demand test either! Yes, I know better!
FYI, my old notes on my pool volume were way off. It isn’t 12,000 gallons, it is 8,500!

 

[Flboy44]

Where did you get those TA numbers? Those didn't come from your Taylor test kit.

Correct, pool store! My testing today is what I expect. Taylor/ strips/ and cheap PoolMaster test- yes, I did all three- say, 70-80 TA
Pool store today says 41! We discussed the difference and they said their test is adjusted for the CYA. This puts us in agreement! But— with an adjusted 41, still shooting for a range of 80-120, where is the compensation of values between adjusted/raw readings? Am I making sense?

 

[mknauss]

Do not use an adjusted TA for anything.

TA above 50 is fine.

 

[Mdragger88]

Just so you’re understanding- ph & ta are married chemically, any chemical you add to lower or raise one will affect the other.

TA - Further Reading

www.troublefreepool.com

 

[mgtfp]

As you probably read by now from the article linked above, the adjustment means that TA is reduced by roughly 1/3 CYA (exact factor is pH dependant, but always around 1/3 for normal pool pH). The only time when that is required is when doing a manual calculation of the CSI. By subtracting the Alkalinity contribution made by CYA you get Carbonate Alkalinity, which can get be used to calculate the amount of dissolved Carbonate in the water, which can then be used to calculate the CSI, which tells you if your pool is at risk of forming scale (aka Calcium Carbonate), or bring aggressive to a plaster surface.

No one does these calculations by hand anymore, you just plug all the required parameters as tested with your test kit into a calculator app like PoolMath and get the result. PoolMath does the above mentioned calculation of the Carbonate Alkalinity internally and uses it for the CSI calculation. There is absolutely no need to show the Carbonate Alkalinity value to the app user, it just creates confusion. All contributors of Alkalinity are "real" Alkalinity, that's why they show up in the TA test. It is the Total Alkalinity that quantifies the buffering capability of your pool water against pH dropping, and not some sort of adjusted Alkalinity.

Showing "adjusted" Alkalinity to the customers is IMHO only a pool store tactic to make Alkalinity look lower to sell them overpriced baking soda to make them chase TA targets that are unnecessarily high to start with for most pools (unless solely Trichlor and Dichlor are used for chlorination, which isn't a good idea for other reasons).