# Trying to understand Alkalinity and Power of Hydrogen (pH) scale

#### Waiawa

Silver Supporter
So if pH is a scale of acid (1) and alkaline (14), why do we say we need to raise/lower...the scale (pH)?

I'm probably thinking too much on this and keep getting on Rabbit trails, but it seems we would say to raise/lower your acid or alkaline being pH is a scale of the two.

Thank you!

#### YippeeSkippy

The pH scale goes from 1 to 14, with 7 being "neutral". So a pool test of 6.7 is acidic, and a pool test of 8.5 is alkaline or base.

Your skin is for the most part around 7.5, but your stomach acid is like 2.4.

#### mgtfp

Bronze Supporter
You are correct that pH is a measure for how acidic or alkaline a watery solution is. It quantifies the concentration of H+ ions in the water (actually, it's H3O+) on a logarithmic scale. pH=7 means neutral, <7 acidic, >7 alkaline.

Alkalinity (as in Total Alkalinity) on the other hand is not a measure for how acidic or alkaline your pool water is, but measures (in ppm, not logarithmic) the concentration of molecules in the water that act as a buffer, i.e. limit the change in pH when adding an acid or a base.

#### Waiawa

Silver Supporter
Sorry if this is really not that important, I'm just trying to understand what the lingo really means.
At least I learn what pH means now...you're not asking what my ph number is!
Thank you very much for your explanation on the matter.

#### mgtfp

Bronze Supporter
Sorry if this is really not that important, I'm just trying to understand what the lingo really means.

Yes that's it, it is a number that tells you if water is acidic, neutral or basic.

Let's dive down a bit deeper to decode the lingo (or just ignore everything below this line, if you are happy with the above):

In any vessel containing water you have an equilibrium reaction going on: H2O + H2O <=> H3O+ + OH- (sometimes that gets simplified to H2O <=> H+ + OH-).

Without any added acids or bases, you have in equilibrium same amounts of H3O+ and OH-, in concentrations of 10-7 mol/L: [H3O+] = [OH-] = 10-7 mol/L (the notation [a] means "concentration of a", "mol" is the unit that chemists use to count molecules, and "Liter" is used as the SI-unit for volumes, 10-7 is the same as 0.0000001, but a bit more convenient, it tells you immediately that there are 7 zeros involved rather than having to count them).

When you add an acid to the water, this equilibrium changes, and you get more H3O+ and less OH-, but in the new equilibrium the product of both concentrations still remains 10-14 (always). You get e.g. [H3O+] = 10-10 mol/L and [OH-] = 10-4 mol/L.

The concentration of H3O+ is used as a measure for how acidic (if [H3O+] > 10-7 mol/L) or basic (if [H3O+] < 10-7 mol/L) the watery solution is.

Now, it's bit of a mouthful to always speak of [H3O+] = 10-x mol/L - all you are really interested in, is the "x". To get that, you have to take the logarithm (to the base of 10) of [H3O+] in the units mol/L, and multiply with -1 to (usually) get a positive number (just out of convenience). And then call it pH, i.e. pH = x.

Or in the full formula: pH = -lg([H3O+]/(1 mol/L)).

In neutral water without any added acids or bases, you have therefore pH=7, which is just another notation for [H3O+] = 10-7 mol/L.

If you add an acid like muriatic acid (HCl), it will release H+ which will grab some H2O to form more H3O+, i.e. [H3O+] > 10-7 mol/L, or pH < 7 (remember the "-" in the pH-formula). Some of the OH- will also grab some H+ to from H2O to ensure the product of [H3O+] and [OH-] remains 10-14.

A base like caustic soda (NaOH) will release some OH-, some of this excess OH- will grab some H+ from H3O+ and form H2O, ensuring that the product of [H3O+] and [OH-] remains 10-14, resulting in [H3O+] < 10-7 mol/L, or pH > 7 (there are also different types of bases that don't release OH-, but directly grab some H+ from H3O+).

Hope that clarifies a bit what pH means - and that I didn't just create confusion. In the end, pH is just a measure for how many H3O+ molecules are in the water, and that's what makes it acidic - H3O+ activates (although not directly as far as I know, it's a bit more complicated) the "sour" taste receptors on your tongue.

HermanTX and Waiawa

#### JJ_Tex

Gold Supporter
Bronze Supporter
Sorry if this is really not that important, I'm just trying to understand what the lingo really means.
At least I learn what pH means now...you're not asking what my ph number is!

I'm not one to be accused of overthinking things, but I think you are WAY overthinking this.

Yes, pH has a scale, but you have an actual number value for your pH at that given moment. To lower your pH value, you add acid. To raise your pH value you add a base like baking soda.

Its really no different than temperature. There are F/C temperature scales, but everything has a temperature that is an actual value on that scale. The inside of your house is a certain temperature, and you can lower it by turning on the A/C or raise it by turning on the heater. If I ask you what the temperature is outside, I'm literally asking you for the value of the air on the F or C temp scale.

Last edited:

#### Waiawa

Silver Supporter
Yes that's it, it is a number that tells you if water is acidic, neutral or basic.

Let's dive down a bit deeper to decode the lingo (or just ignore everything below this line, if you are happy with the above):

In any vessel containing water you have an equilibrium reaction going on: H2O + H2O <=> H3O+ + OH- (sometimes that gets simplified to H2O <=> H+ + OH-).

Without any added acids or bases, you have in equilibrium same amounts of H3O+ and OH-, in concentrations of 10-7 mol/L: [H3O+] = [OH-] = 10-7 mol/L (the notation [a] means "concentration of a", "mol" is the unit that chemists use to count molecules, and "Liter" is used as the SI-unit for volumes, 10-7 is the same as 0.0000001, but a bit more convenient, it tells you immediately that there are 7 zeros involved rather than having to count them).

When you add an acid to the water, this equilibrium changes, and you get more H3O+ and less OH-, but in the new equilibrium the product of both concentrations still remains 10-14 (always). You get e.g. [H3O+] = 10-10 mol/L and [OH-] = 10-4 mol/L.

The concentration of H3O+ is used as a measure for how acidic (if [H3O+] > 10-7 mol/L) or basic (if [H3O+] < 10-7 mol/L) the watery solution is.

Now, it's bit of a mouthful to always speak of [H3O+] = 10-x mol/L - all you are really interested in, is the "x". To get that, you have to take the logarithm (to the base of 10) of [H3O+] in the units mol/L, and multiply with -1 to (usually) get a positive number (just out of convenience). And then call it pH, i.e. pH = x.

Or in the full formula: pH = -lg([H3O+]/(1 mol/L)).

In neutral water without any added acids or bases, you have therefore pH=7, which is just another notation for [H3O+] = 10-7 mol/L.

If you add an acid like muriatic acid (HCl), it will release H+ which will grab some H2O to form more H3O+, i.e. [H3O+] > 10-7 mol/L, or pH < 7 (remember the "-" in the pH-formula). Some of the OH- will also grab some H+ to from H2O to ensure the product of [H3O+] and [OH-] remains 10-14.

A base like caustic soda (NaOH) will release some OH-, some of this excess OH- will grab some H+ from H3O+ and form H2O, ensuring that the product of [H3O+] and [OH-] remains 10-14, resulting in [H3O+] < 10-7 mol/L, or pH > 7 (there are also different types of bases that don't release OH-, but directly grab some H+ from H3O+).

Hope that clarifies a bit what pH means - and that I didn't just create confusion. In the end, pH is just a measure for how many H3O+ molecules are in the water, and that's what makes it acidic - H3O+ activates (although not directly as far as I know, it's a bit more complicated) the "sour" taste receptors on your tongue.
Now that was the long story...which most just went over my head, but never the less, I did read it all.
So I'm thinking the short story would be when asked what my pH is, it is the value of the pH scale of Acidity or Basicity.

Thank you for your time to type the needed information.

#### Donldson

TFP Expert
Now that was the long story...which most just went over my head, but never the less, I did read it all.
When someone asks a question that far in to the weeds then it's generally assumed they have the base knowledge required to comprehend the answer.

When someone asks what your pH is we are asking what your pH test says. Quite a few of us have the ability to interpret results and chemical dosages with only a fairly shallow understanding of the science behind it. I don't understand everything about lithium ion power storage but I can still drive my car well enough to not get my insurance company angry.

#### jseyfert3

Silver Supporter
Bronze Supporter
TFP Guide
So if pH is a scale of acid (1) and alkaline (14), why do we say we need to raise/lower...the scale (pH)?

I'm probably thinking too much on this and keep getting on Rabbit trails, but it seems we would say to raise/lower your acid or alkaline being pH is a scale of the two.
So I'm thinking the short story would be when asked what my pH is, it is the value of the pH scale of Acidity or Basicity.
A pH is a measurement of a specific property of a liquid. When you take this measurement, you get a specific number. If you measure pure water, you will get a pH measurement of 7. If you measure orange juice, you will get a pH measurement of 3.5. If you measure ammonia, you will get a pH measurement of 11.5. Note that when you measure different liquids, you get a different number. In all cases, this number is the pH.

Now, let's think of a scale. A scale is just a defined set of numbers. For example, when someone asks you on a scale of 0-10, how satisfied are you, with 10 being perfectly satisfied and 0 being completely unsatisfied, what they are saying is that they want you to choose a number between 0-10. 0-10 is the scale of satisfaction. So if someone asks you "how satisfied are you" and you say you are 0, that means you are unsatisfied and will post on facebook saying how terrible something was. If you say you are 5, that means you are "meh." and if you say 10, that means you are so satisfied you will tell all your friends about it.

Now we go back to pH. It turns out that when you measure pH, all the values fall within 0 to 14. So therefore 0 to 14 was defined to be the scale of pH, just as 0-10 was the scale of satisfaction in the above example. When someone asks what your pH is, they want you to say a number between 0 and 14, just as in the above example they wanted you to say your satisfaction as a number from 0-10. In one case, they want a number of the scale of pH, the other case, they want a number on the scale of happiness. Make sense?

Now, consider again the scale of satisfaction. If 5 is "meh", then any answer between 0 and 5 means you are unsatisfied, and any answer between 5 and 10 means you are satisfied. This is similar to the scale of pH, where 7 is considered neutral. Anything between a 0 and 7 is considered acidic, and anything between 7 and 14 is considered basic. So when someone asks you what the pH of your orange juice is, the answer is that the pH is 3.5. But because the pH is 3.5, the orange just is considered acidic. Similarly if someone asked you what the pH of your cleaning ammonia is, the answer is 11.5. Because the pH is 11.5, the ammonia is considered basic.

In other words, it's is not the scale of acidicy and basicity, it is the scale of pH. But certain values are either acidic or basic, depending on what they are. That is why we say we need to raise or lower the pH, and not raising or lowering your acidity or basicity. Does that make sense?

NCMike

#### mgtfp

Bronze Supporter
Now we go back to pH. It turns out that when you measure pH, all the values fall within 0 to 14. So therefore 0 to 14 was defined to be the scale of pH, just as 0-10 was the scale of satisfaction in the above example. When someone asks what your pH is, they want you to say a number between 0 and 14, just as in the above example they wanted you to say your satisfaction as a number from 0-10. In one case, they want a number of the scale of pH, the other case, they want a number on the scale of happiness. Make sense?

Unfortunately, many text books get that wrong, or at least don't clarify that sufficiently, but the pH-scale is open ended, not limited to 0-14. There is no physical reason, why [H3O+] > 1 mol/L (= 10-0 mol/L) shouldn't be possible.

For example, 32% MA has a pH of -1.

Problem is, that it is not easy to measure. But my pH-meter is specified to work in the range -2 to 16 (never tried that, don't really fancy dipping it into straight MA).

jseyfert3

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#### jseyfert3

Silver Supporter
Bronze Supporter
TFP Guide
Unfortunately, many text books get that wrong, or at least don't clarify that sufficiently, but the pH-scale is open ended, not limited to 0-14. There is no physical reason, why [H3O+] > 1 mol/L (= 10-0 mol/L) shouldn't be possible.
Yeah I know, but I was trying to keep it slightly easier to understand, and 0-14 is most commonly quoted. My satisfaction analogy kind of breaks down if you say pH isn't limited to 0-14...then again on second thought, maybe not, cause I've often heard people respond "11" to a question of "on a scale of 0-10" type questions, or even negative, in certain extreme cases. So, I suppose my analogy still works.

Donldson and mgtfp

#### Waiawa

Silver Supporter
I get it...like what's your weight on a "weight" scale?
What's your pH on the pH scale?
I guess it's easier to say your pH is too high/low than to say your pH is too acidic/basicity.

jseyfert3

#### mgtfp

Bronze Supporter
I get it...like what's your weight on a "weight" scale?
What's your pH on the pH scale?
I guess it's easier to say your pH is too high/low than to say your pH is too acidic/basicity.

That's it. Apart from FC it is one of the most important parameters in pool water chemistry.

The other parameters we test for are kind of secondary parameters to make FC and pH work.

CYA for example is important to protect FC from UV.

TA is important to stop pH from fluctuating (but a TA that's too high will result in pH drifting upwards, an effect that needs to be separated from pH fluctuations when TA is too low).

And CH is particularly important for plaster pools to protect them from plaster dissolving into the water - CH needs to be high enough to make the water at the target values for pH and TA (and CYA) non-corrosive to plaster. But you don't want it too high (for any type of pool) to avoid scaling. Which is where CSI comes into play, a number calculated from the other parameters quantifying the scaling/corrosion potential of water.

If something goes out of whack, you first worry about FC, then pH. Then you can start thinking about the other parameters.

All you need to do is to keep parameters in the TFP recommended ranges, no need to chase "the" perfect value. Over time you will learn what works best for your pool.

#### YippeeSkippy

If I ask you "what's your pool's pH?" all I expect you to say is "7.5" or something like that.

I can interpret it on the spot to know if its too acidic or too alkaline.

#### Waiawa

Silver Supporter
If I ask you "what's your pool's pH?" all I expect you to say is "7.5" or something like that.

I can interpret it on the spot to know if its too acidic or too alkaline.

Right now it's at 7.6 from what I can see/color match.
CL is about 3.5 - 4.0 not sure, but darker than the matching color on the vial.
I'm hoping for my TFtestkit to arrive soon, according to the tracking number it departed Creedmoor, NC post office at 5:07pm.
Hopefully it arrives sooner than later. I'm wanting to test my CYA, CC and CH.

Mdragger88

7.6 is a nice pH

#### Waiawa

Silver Supporter
My TA is at 110, seems like that's too high according to the pool school recommendations.
I may mess with it tomorrow if it doesn't rain.

#### YippeeSkippy

Please wait.... don't jump the gun. Each pool has its own chemistry "personality". You might find your pool lingers at a pH of 7.6ish even with the TA of 110.
Only play with the TA if your pH is unstable for where you want the pH. Wait and see if it remains steady or raises.

mgtfp

#### Waiawa

Silver Supporter
Ok, will do...Thank you!

I got my eyes turning red reading all the articles in Further Reading....sheesh!
This place is a Pool Owner's Library!

Mdragger88

#### mgtfp

Bronze Supporter
As Maddie said, no rush with TA. If your pH doesn't drift up beyond 8 quickly, 110 can be fine. There is certainly no need to add baking soda to get it even higher as pool shops might ask you to do. And you certainly want your TA verified with your TF100 before adjusting anything (that applies to all parameters).

Next step will be to test CYA once your test kit arrives and make sure that your FC is matching your CYA according to the FC/CYA Chart.

If your CYA turns out to be way too high, you might want to dump some water to get CYA down. If you have to do that, it would be wise to also consider CH - you don't want to first dump and refill to get CYA right, and then realise that you have to dump more water to get CH right.

If CYA turns out to be too low, you don't have to rush, even in TX the UV will right now be at its lowest.

Once FC is adjusted according to your CYA and maintained there, any potential CC should disappear pretty quickly. Unless you have an algae problem consuming your FC as you add it, then you needed to SLAM.

But we'll cross all these bridges when we get there, i.e. when your test kit arrives.

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