pH non-existant/alkalinity?

[DeeDee]

pH - Bright yellow TA - ?
FC - 7.5
CYA - 42
CH - 375
I went away for Christmas and filled my chlorine dispenser with too much chlorine. When I returned 3 weeks later, the chlorine was sky high. I turned it off and it has come down, but when I test the TA, it turns bright red immediately (never green) and the pH is bright yellow. I'm now running the pump and bubblers to aerate, but I'm confused as to what else I should do. Btw, I do use the Taylor testing kit that you recommend.

 

[JamesW]

I would add about 25 pounds of baking soda and brush and circulate well.

Retest in 1 to 2 hours.

 

[Donldson]

Aeration doesn't raise pH in the absence of TA, the pucks crashed your pH and TA and the water is now about as acidic as vinegar.

Definitely follow JamesW's advice ASAP. Acidic water is bad on just about everything, especially pool surfaces.

 

[DeeDee]

I would add about 25 pounds of baking soda and brush and circulate well.

Retest in 1 to 2 hours.

I did it and the TA is 10. Should I just continue to add 25 pounds of baking soda and circulating?

 

[JamesW]

Add another 20 pounds of baking soda.

 

[DavidLast]

Try using soda ash/ sodium carbonate instead of baking soda, This will raise the TA faster when the TA is completely exhausted.

 

[JamesW]

Try using soda ash/ sodium carbonate instead of baking soda, This will raise the TA faster when the TA is completely exhausted.

That has a much higher risk of creating adverse effects.

Baking soda is a safer choice.

 

[DavidLast]

That has a much higher risk of creating adverse effects.

Baking soda is a safer choice.

However in 0 TA the baking soda will not work properly.

 

[JamesW]

However in 0 TA the baking soda will not work properly.

Why not?

It will work just fine.

 

[DavidLast]

pH

 

[JamesW]

I did it and the TA is 10.

25 pounds will raise the TA by 75 ppm.

The TA started at - 65, so adding 25 pounds increased the TA from -65 to 10.

Adding 20 pounds should result in a TA increase of about 60 ppm or a new TA of about 70.

The pH will be out of the danger zone.

 

[JamesW]

Baking soda raise the pH just fine from low pH into the 7s without risking overshooting the safe pH range.

 

[JamesW]

pH

Explain with chemical equations.

 

[DavidLast]

25 pounds will raise the TA by 75 ppm.

The TA started at - 65, so adding 25 pounds increased the TA from -65 to 10.

Adding 20 pounds should result in a TA increase of about 60 ppm or a new TA of about 70.

The pH will be out of the danger zone.

This is the issue.

Why add hydrogen when pH is already saturated with hydrogen? The baking soda wont work as expected in 0 TA. Add soda ash to take up some hydrogen and then baking soda will work.

 

[JamesW]

HCO₃^- + H⁺ --> H₂CO₃ --> H₂O + CO₂

The bicarbonate converts into carbon dioxide like this and the pH rises because you are removing free hydrogen ions.

The carbon dioxide offgasses and is lost.

The amount of carbon dioxide created determines the rate of pH rise.

The amount of carbon dioxide depends on the pH and the TA.

There is always a specific percentage of the TA that turns into carbon dioxide.

pH....................%CO2
7.0........................18.292
7.1........................15.097
7.2........................12.377
7.3........................10.088
7.4........................8.183
7.5........................6.611
7.6........................5.324
7.7........................4.275
7.8........................3.426
7.9........................2.741
8.0........................2.189
8.1........................1.747
8.2........................1.392
8.3........................1.109

You can use the formulas to calculate the percentage of bicarbonate vs. carbon dioxide or carbon dioxide vs. bicarbonate.

100÷(1+10^(6.35 – 8.3)) = 98.890% bicarbonate vs. carbon dioxide.

100-(100÷(1+10^(6.35 – 8.3))) = 1.109% carbon dioxide vs. bicarbonate.

plot y = 100÷(1+10^(6.35 – x)) and y = 100-(100÷(1+10^(6.35 – x))), x from 4 to 9 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[DavidLast]

Much faster using carbonate. It converts to bicarbonate and lifts the TA and pH quickly then raise the TA when you have a reading.

 

[JamesW]

As you can see, the baking soda converts into carbon dioxide quite a bit when the pH is low and this raises the pH.

The effect automatically slows down as the pH rises and this make the process much safer than using sodium carbonate, which can cause scaling and clouding.

pH............%CO2
4.0..............99.555
4.5..............98.607
5.0..............95.724
5.5..............87.6229
6.0..............69.1236
6.35...........50.000
6.5..............41.45
7.0..............18.292
7.5.............6.6114

 

[JamesW]

Much faster using carbonate.

Not really.

Baking soda works just as fast and it is much safer.

The reaction is pretty much complete as fast as the baking soda gets mixed in the water.

 

[JamesW]

CO₃^2- + 2H⁺ --> H₂CO₃ --> H₂O + CO₂.

For carbonate, it picks up 2 hydrogens, but it still results in the same thing.

The risk is an excessive pH locally and the carbonate can combine with calcium to form calcium carbonate clouding.

CO₃^2- + Ca²⁺ --> CaCO₃

Carbonate plus calcium = calcium carbonate.

 

[DeeDee]

I am so thankful that ya'll understand all of this and I get your guidance. Thank you!