pH won’t go down in hot tub.

[Srbinette]

New hot tub owner. Trying to balance chemicals. I cannot for the life of me get my pH down. It has been at or over 8.0 for several days despite adding acid. Water is crystal clear. Any suggestions? Do I keep adding acid every few hours until it works?

pH 8.0+
TA 70
CH 150
CYA <30

 

[Bperry]

New hot tub owner. Trying to balance chemicals. I cannot for the life of me get my pH down. It has been at or over 8.0 for several days despite adding acid. Water is crystal clear. Any suggestions? Do I keep adding acid every few hours until it works?

pH 8.0+
TA 70
CH 150
CYA <30

Yea, target 7.2 and add what pool math says to get it there, then check again 10 minutes later. Then do it again until it reads in the 7’s.

 

[Mdragger88]

Like @Bperry said- don’t wait hours- it will have risen again. 10 minutes is plenty.

 

[98Poolmaster]

Like @Bperry said- don’t wait hours- it will have risen again. 10 minutes is plenty.

How fast does aeration raise the pH guys?what she has is a 375 gallon Caldera Vanto (if that makes a difference in the speed of raising her pH)

 

[Mdragger88]

How fast does aeration raise the pH guys?what she has is a 375 gallon Sundance Vanto (if that makes a difference in the speed of raising her pH)

With the jets going 30 minutes or so. I can get my ta lowered from 110 to 60 in a day if I am vigilant about adding acid every 30 minutes to an hour after aerating

 

[98Poolmaster]

With the jets going 30 minutes or so. I can get my ta lowered from 110 to 60 in a day if I am vigilant about adding acid every 30 minutes to an hour after in

With the jets going 30 minutes or so. I can get my ta lowered from 110 to 60 in a day if I am vigilant about adding acid every 30 minutes to an hour after aerating

Thank you

With the jets going 30 minutes or so. I can get my ta lowered from 110 to 60 in a day if I am vigilant about adding acid every 30 minutes to an hour after aerating

Thank You very much don’t know why I put Sundance hers is a Caldera(I edited it to the correct brand)I was just dealing with a customer today about her Sundance guess I have that brand on my mind sorry to ramble but I appreciate your input

 

[Srbinette]

Tested, retested and added acid every 15-30 minutes tonight. Very little improvement in pH (still looking like 8.0+, however just one drop of acid demand brings it to 7.4, so getting closer). It lowered my Alkalinity from 70 to 50. I’ll try again tomorrow. Although I’m worried I’ll need to increase alkalinity and I’ll be back at a high pH.

 

[Mdragger88]

Now that your ta is lower just aim for mid 7’s (7.6) with the acid as to not lower the ta as much. If ta goes to 40 raise it back up to 50 with a little baking soda

 

[Srbinette]

Was able to get pH down to 7.6 but alkalinity was only at 30 (which is basically where I started from the tap). Decided to add more baking soda. Got alkalinity up to 100, now I’m adding acid to drop pH from 8+ to hopefully somewhere in the 7s. I’ll let you know how it goes.

 

[JamesW]

Heat and aeration cause the carbon dioxide to come out pretty fast.

Basically like shaking a can of soda or beer or letting them sit out and get warm.

Low TA does not matter as long as the pH is good.

 

[JamesW]

The amount of carbon dioxide 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.

So, if you keep the TA low and the pH high, the Carbon Dioxide levels will be low enough to reduce pH rise to a manageable level.

I would target a pH of about 7.9 and let the TA do whatever it does.

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

As you can see, the amount of carbon dioxide is about 8.35 times higher at a pH of 7.0 compared to a pH of 8.0.

That means 8.35 times as much pH rise.

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

 

[JamesW]

Percentage bicarbonate.



_____________________________________________________________________________________

Bicarbonate vs. carbonate.




_____________________________________________________________________________________

Carbon dioxide vs. Bicarbonate.



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.

 

[Srbinette]

Been working at it for the last hour and a half. Got the pH to 7.8 and alkalinity is at 60. I think that’s about as good as it’s going to get. I’m calling it.

 

[JamesW]

Watch the CSI and do not let it get too high.

Hot water is more prone to scaling, especially on the heater element.

If the CSI is 0.0 or lower, the pH and TA are good.

If the CSI is over 0.0, lower the pH to lower the TA.

 

[Mdragger88]

In the future be a dab more light handed with the baking soda if its ever needed again. A little goes a long way. You can always add more if you need to. The recommendation of 50 or above is to prevent ph bounce. Some folks are able to keep ta at 40 without this happening.
There is no “perfect” ph or ta for that matter.
Ph in the high 7’s is fine - no need to try & force it lower. Pushing it to the low 7’s just makes it climb faster.
Many find their ph will hang around the high 7’s or even 8.0 for some time before going higher. For this reason I prefer a ph comparator that goes to 8.2. Prevents the freak outs a little when on the line.
Note* if you decide to get one of those it takes a different reagent than the one that goes to 8.0.