pH Insanity!

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M

matgeek

New member
Mar 16, 2024
3
Simcoe, Ontario, Canada
Hey All,

Long time listener, first time caller... TLDR; no matter how low I take my Alkalinity, my pH always jumps back above 8.

I've had a Chlorine tub for the last year or so and have struggled to get the pH within range the whole time - I've recently switch to Bromine for mostly unrelated reasons and am seeing the same behaviour.

I'm using a Taylor CK-2006 test kit, which is how I measured all values below.

Hot Tub Details:
  • Hot Springs Sovereign - 330 gallons (1250 liters)
  • 3x Pumps (1x heater loop, 2x jets)
  • 1x Diverter Valve

Water from my tap (filtered through an inline metal remover or not):
  • FC: ~1ppm
  • pH: 7.4
  • Alkalinity: 200ppm
  • Calcium Hardness: 200ppm
  • CYA: 0ppm

Obviously the first order of business is to get the Alkalinity down, so I add enough pH Down to get the Alkalinity to 80ppm while running my jets on full with the diverter valve set to flow water through both loops 50/50 (I don't have an air valve to close, so I just run it)... One would think this would tank the pH below 7, but by the time I'm done mixing for 20 minutes, the pH is already above 8.0.

I've tried adding enough pH down to get it where I want (7.4 is my target), which brought my Alkalinity to literally 0ppm, and after adding enough baking soda to bring my Alkalinity back to 50ppm, my pH shot way above 8 immediately.

I've read a lot about Borates, but it looks like they are only effective in situations of low pH... so I'm at a total loss at this point and wondering if any of you more experienced folks have some advice for this lost Canadian?
 
I guess I should ask, if my pH is stable at 200ppm Alk, should I bother adjusting it? Will I be creating a ton of scale or something else detrimental to my tub?

Just picked up some Muriatic Acid, will refill this afternoon and give biggen’s suggestion a try.

Thank you @mknauss for the storage recommendation, will keep it in its own 5gal pale with lid affixed and stored outside.
 
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@matgeek
Ph will always be rising in a hot tub. Its just part of having a small body of water with lots of aeration.
The addition of borates can help mitigate it some.
I think you’re probably talking about borax for low ph purposes.
While borax is a product with borates in it, we recommend using boric acid for adding borates as it doesn’t have the ph increasing effects of borax which would need to be offset by additional acid.

Borates in pool - Further Reading

www.troublefreepool.com www.troublefreepool.com
I suspect you were a little heavy handed with the dry acid. It is easy to overshoot chems in a small tub as there’s not alot of wiggle room. That’s ok - you corrected it 👍🏻
less is more until you have it dialed in. You can always add more later.
Most find that a ta of 50 is ideal in their tub to help mitigate the ph rise some. Some are ok at 40 & some at 60.
Each tub is a little different. Once ta is near your target (50/60 range) you would add the boric acid.
Be sure to include your borate level in poolmath so it calculates your future acid additions properly.

Once you’re at the target ta just aim for ph in mid 7’s when dosing. Going lower may cause you to accidentally lower ta.
Other things you can do:
Be sure the tub is filled so the jets aren’t exposed & causing as much turbulence when the circ pumps run during standby times.
This can be a challenge due to splashout.

Reduce pump run times during standby. (Most have some kind of filtering schedule that is adjustable.)

Be sure to check the ph when the water has been calm for an accurate baseline.
 
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If it makes you feel any better I am in the same boat. If I want pH below 8 I have to live with TA of 50 or lower. I use MA to reduce pH and baking soda to try to increase TA.
 
Maybe I am confused but does TA buffer PH. It seems like several posts are using PH and TA interchangeably. I run around 50 TA on a 500 gallon spa and adding anything more than like 1 oz of acid will drop PH below 7.4. I don't have adjust my PH very often with a TA of 50-60.
 
I am using baking soda to raise my TA, but it raises pH as well. To reduce pH I use MA, but it causes my TA to plummet.
 

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wayner said:
I am using baking soda to raise my TA, but it raises pH as well. To reduce pH I use MA, but it causes my TA to plummet.
Click to expand...
Sounds like you’re using too much acid to lower ph (aka lowering ph too low)
Only aim for ph in mid 7’s (7.6 or higher) when ta is 60 or below.
No need for baking soda unless ta is 40 or less. Note* Some tubs are fine & stable with a ta of 40.
No need to micromanage ph - if it hangs out at 7.9/8.0 a while that’s ok. When it gets closer to 8.2 lower back to 7.6/7.8 without affecting ta too much.
 
I add pretty small amounts of acid to get my pH down to about 7.5. It rarely gets lower than that. And my TA tends to sit around 30-40 when my pH is below 8.
 
maverick69 said:
Maybe I am confused but does TA buffer PH. It seems like several posts are using PH and TA interchangeably. I run around 50 TA on a 500 gallon spa and adding anything more than like 1 oz of acid will drop PH below 7.4. I don't have adjust my PH very often with a TA of 50-60.
Click to expand...
They are “married” when it comes to chemicals - what lowers one will lower the other in some way & what raises one will raise the other in some way. The only exception is aeration which increases ph without increasing ta.
Yes - ta is a buffer if you will for ph- to keep it from falling too low.
If ta falls below 40ppm ph can drop very low & an acidic condition can occur.
The lower the ta the more the ph is affected by the same acid addition all other things being equal.
Borates also provide some buffer for ph by helping “hold it down” some - this explains why you need more acid to get the same result when you have Borates in the water.
I find my ph rise rate to be very reasonable & predictable when my ta is 50/60 especially when using borates in the 30-50ppm range.
 
maverick69 said:
Maybe I am confused but does TA buffer PH. It seems like several posts are using PH and TA interchangeably. I run around 50 TA on a 500 gallon spa and adding anything more than like 1 oz of acid will drop PH below 7.4. I don't have adjust my PH very often with a TA of 50-60.
Click to expand...

TA is an indicator for the buffering capability of the water. The higher the TA, the smaller the pH-drop by an acid addition.

The hydrogen ions from the added acid (MA is HCl which is a strong acid that fully splits into H+ and Cl- when added to water) are "buffered" by finding those ions that count towards the TA-value and attaching to them rather than floating around as free hydrogen ions. pH is essentially a measure for the number of free hydrogen ions in the water, the lower the pH the higher the number of free H+ ions.

But when it gets to pH-rising, then "more TA" will not make it better, due to Carbonate Alkalinity being the main contributor to Total Alkalinity, and more Carbonate = more CO2 outgassing = faster pH-rise.
 
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mgtfp said:
TA is an indicator for the buffering capability of the water. The higher the TA, the smaller the pH-drop by an acid addition.

The hydrogen ions from the added acid (MA is HCl which is a strong acid that fully splits into H+ and Cl- when added to water) are "buffered" by finding those ions that count towards the TA-value and attaching to them rather than floating around as free hydrogen ions. pH is essentially a measure for the number of free hydrogen ions in the water, the lower the pH the higher the number of free H+ ions.

But when it gets to pH-rising, then "more TA" will not make it better, due to Carbonate Alkalinity being the main contributor to Total Alkalinity, and more Carbonate = more CO2 outgassing = faster pH-rise.
Click to expand...
What I wanted to say, but didn't know how to say it.

Great explanation.

Higher TA levels makes whatever PH you currently have more "sticky" or harder to change. IE Buffering.
 
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Mdragger88 said:
Are you using borates?
Click to expand...
No borates. The only thing I have in my tub is tap water salt and MA. Occasionally I add a bit of baking soda to get TA up but it usually screws up my pH. So I continue to live with TA of 40-50. If I remember to close the air intake then the pH just increases very slowly - it stayed around 7.5 all week since I tested last Sunday.
 
wayner said:
No borates. The only thing I have in my tub is tap water salt and MA. Occasionally I add a bit of baking soda to get TA up but it usually screws up my pH. So I continue to live with TA of 40-50. If I remember to close the air intake then the pH just increases very slowly - it stayed around 7.5 all week since I tested last Sunday.
Click to expand...
Ta of 40-50 is totally ok 👍🏻 so long as things r pretty stable. Under 40 you may experience “ph bounce”. So long as its working for you its fine.
You can try adding the 50ppm borates via boric acid & see if it lends you a helping hand with the rise - the addition is a little acidic so I add it when my ph is a little higher. Check poolmath effects of adding first if you intend to try it.
 
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