TA, PH and muriatic acid playing together

[emac]

I have a new plaster pool. 28K gal. Thanks to this site I have kept the pool clear as a bell all year with no issues. I am a bit addicted to testing and the numbers. My wife calls me the mad scientist. I find it fun. I installed a Liquidator, that works pretty well. Gets some scaling in it, but that may be due to my PH running on the higher side. The Liquidator manual suggests keeping the PH around 7.3. That is hard for me.

My builder said I will have to add acid pretty often for up to a year as the plaster cures out. My PH will climb to 7.8 after several days, so I add acid pretty often (a few times a week). My TA has recently dropped to 64. I have added baking soda a few times and I try to keep the TA closer to 80. Ok heres the question:

Is it ok to add acid and baking soda at the same time or back to back? I realize they work opposite on PH. So I try to keep the PH balanced. Does adding acid negate the baking soda/TA or does the TA climb by just having the baking soda added. Does the baking soda add to the TA even if it gets balanced by the acid?

Did that make sense?? Am I overthinking?

Thanks in advance.

 

[denniswiseman]

Adding muriatic acid will lower pH and TA, baking soda only raise TA
Mainly concentrate on pH, then the TA. Although it has been suggested here to not raise the TA to high to help stabilise the pH

 

[emac]

Ok, after some more reading, and your post it makes better sense. Thanks. Soda ash is a stronger base to raise PH. Baking soda will raise PH, but not as effectively as soda ash. I had it in my mind that baking soda was the way to raise PH. I dont have experience raising PH!

I have a slide rule that calculates the CSI based on temp, ph, TA, CH. It really helps me understand how each contributes to the CSI.

 

[denniswiseman]

You could try aeration to raise pH only
I use this when I have to
This has no other effect on TA

 

[pooldv]

PoolMath, link at top of page, will calculate your CSI. More here about pool chems and what they do, Pool School - Recommended Pool Chemicals

More here about pH and TA
ABCs of Pool Water Chemistry

 

[emac]

Thanks, I have read those a ton of times and use the CSI/pool calculator. Very helpful. I like the slide rule, because you can see how just raising temp, or other parts, changes the formula.

I was interested in how TA (baking soda) and acid interact.

 

[JamesW]

Don't raise the TA. Lower the pH to 7.8 as needed. If you stop adding baking soda, your pH will become much more stable.

Try a TA of 60 and a pH of 7.8 for a while. Your acid demand will fall by more than half.

Try to keep the CSI at -0.2 to 0.0.

Basically, the acid and baking soda neutralize each other and you're just wasting both.

If you poured some acid in a bucket and then sprinkled in baking soda, you would get bubbling. That's carbon dioxide. As you keep adding the baking soda, the bubbles eventually stop. Once the bubbles stop, the acid and baking soda are gone and all that's left is water and salt.

The salt is due to the chloride in acid (hydrogen chloride) and the sodium in baking soda (sodium bicarbonate). They're not involved in the reaction and are left behind.

That's pretty much all you're doing.

If your pH is too low and your TA is too high, you get lots of carbon dioxide as they react and neutralize each other.

Low pH creates a lot of H+ (hydrogen ions) and high TA creates lots of HCO3- (bicarbonate ions). They connect to create H2CO3 (carbonic acid), which becomes H2O + CO2.

The CO2 offgasses like a soda going flat and the acid and bicarb are gone leaving nothing but water and salt.

So, you add more, and the cycle continues.

By raising the pH (less H+) and lowering the TA (less HCO3-), your levels stay stable.

As far as CSI goes, higher pH raises CSI and lower TA lowers CSI, so the effect on CSI is roughly neutral.

Some commercial pool operators try to maintain a lower pH and higher TA by injecting carbon dioxide into the water. That creates carbonic acid, which creates H+ and HCO3-. However, they recombine back into carbonic acid and then into carbon dioxide that off gasses and they have to inject more.

They buy tank after tank of CO2 and it's mostly a huge waste of time and money because they don't understand the chemistry or they're following regulations that were written by regulators that don't understand chemistry.

Basically, it's the same thing as adding too much acid and too much bicarb.

 

[emac]

Thanks James, you remind me of a chemistry professor! That is what I was thinking, they are working against each other.

My PH seems to like 7.7, so maybe I should take your advice with it and let TA drop. Thanks for the explanation.