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zapatos

Pool pH and Alkalinity

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I moved into a new home recently and am now the proud (and overworked) owner of an in-ground swimming pool.

Part of pool maintenance is keeping the water chemistry in the correct balance. Two of the things I must regulate are pH and alkalinity; two separate things. Since my water test strips indicate I have low pH AND low alkalinity I had to buy two products to fix the problem. One raises the pH level and one raises the alkalinity level. The product to raise pH contains Sodium Carbonate, and the product to raise alkalinity is sodium bicarbonate.

Since the pH scale is considered acid at one end and alkaline (or base) at the other, I don't understand what it means to raise both pH and alkalinity.

Any help is appreciated.

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It aroused my curiosity, and it seems the alkaline part is a separate buffer to the acid component, which stops the pH wandering and causing damage to the pool, apparently.

https://blog.intheswim.com/pool-ph-alkalinity-tips-for-pool-owners/

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Okay that makes sense. Do you think the way they use the terms pH and alkalinity is correct? Seems like "raise pH" and "raise alkalinity" mean the same thing. Or might they just be playing loose with the terms as it doesn't really matter for the average Joe working on his swimming pool?

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Posted (edited)
42 minutes ago, zapatos said:

Okay that makes sense. Do you think the way they use the terms pH and alkalinity is correct? Seems like "raise pH" and "raise alkalinity" mean the same thing. Or might they just be playing loose with the terms as it doesn't really matter for the average Joe working on his swimming pool?

I'm sure studiot or John Cuthber can give you the low down on that. I know what you mean but my formal chemistry is not up to it. Fwiw it seems to me  it's not just about hydroxyl (OH-) ions but having other alkaline species - anions - as well that buffer. Buffers regulate pH rather than just work in one direction.

Edited by StringJunky

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I've never owned a pool and I'm not a chemist ( disclaimer ).

I've always thought that a pool's pH is kept at a point that is optimal for the 'shock', or oxidizer, that keeps pool water clear.
A strong caustic would be used to bring the pH to that optimal range, and buffering would be used to keep the pH from 'wondering' about.
Otherwise the oxidizer would break down too quickly, and you would have trouble keeping oxidizer level in a safe range.

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In water sciences alkalinity typically refers to overall buffer capacity rather than pH itself, which is a measure of proton concentration. So if you have low alkalinity, small addition of acid would rapidly decrease pH for example.  The main buffer in most environmental systems (and our body) is bicarbonate but other dissolved species can also contribute.

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12 hours ago, StringJunky said:

It aroused my curiosity, and it seems the alkaline part is a separate buffer to the acid component, which stops the pH wandering and causing damage to the pool, apparently.

https://blog.intheswim.com/pool-ph-alkalinity-tips-for-pool-owners/

 

2 hours ago, StringJunky said:

I'm sure studiot or John Cuthber can give you the low down on that. I know what you mean but my formal chemistry is not up to it. Fwiw it seems to me  it's not just about hydroxyl (OH-) ions but having other alkaline species - anions - as well that buffer. Buffers regulate pH rather than just work in one direction.

 

I knew if I looked at Wikipedia long enough I would eventually find something you don't need need to stand on three encyclopedias and a dictionary to read.

Today I found it so here it is

Quote
Alkalinity (from Arabic "al-qalī") is the capacity of water to resist changes in pH that would make the water more acidic. (It should not be confused with basicity which is an absolute measurement on the pH scale.) Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases.

 

pH is a scale that runs from very acid @1ish to very alkaline also called basic @ nearly 14.

Here are some values in relation to common things.

The last one is interesting becasue it shows the range of pH we can safely drink.

 

pH1.jpg.d9193fabaea846ffc4559edf1494be76.jpg

pH2.jpg.78682f79449e5fb9622abb972706dba1.jpg

pH3.jpg.ac13392f0c6ae4ae742843fd688a0655.jpg

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5 minutes ago, studiot said:

 

 

I knew if I looked at Wikipedia long enough I would eventually find something you don't need need to stand on three encyclopedias and a dictionary to read.

Today I found it so here it is

 

pH is a scale that runs from very acid @1ish to very alkaline also called basic @ nearly 14.

Here are some values in relation to common things.

The last one is interesting becasue it shows the range of pH we can safely drink.

 

pH1.jpg.d9193fabaea846ffc4559edf1494be76.jpg

pH2.jpg.78682f79449e5fb9622abb972706dba1.jpg

pH3.jpg.ac13392f0c6ae4ae742843fd688a0655.jpg

Cheers. 'Basicity' is the missing word needed to differentiate.

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Thanks everyone! That makes a lot more sense now.

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2 hours ago, zapatos said:

Thanks everyone! That makes a lot more sense now.

I learnt something too. :)

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