pH vs. Total Alkalinity in Water Chemistry | Orenda Whiteboard

What is the difference between pH and alkalinity?

Many of us in aquatics confuse total alkalinity and pH. It’s understandable, given how similar the words “alkaline” and “alkalinity” are. Indeed, alkalinity and pH are related (pH determines the concentration of Hydrogen, which determines the % of which type of alkalinity you have in water). But pH and alkalinity are not the same.

What is pH?
pH stands for potenz Hydrogen, or more commonly called “power of Hydrogen.” It is the measure of the concentration of hydrogen ions in a solution. We measure how acidic or basic (also called alkaline) substances are by using the pH scale.

pH = -log[H+]. It is a negative logarithm of Hydrogen concentration on a scale of 0-14. Every whole number is 10x the next whole number. 7 is perfectly neutral water. For example, something with a pH of 6 is 10x more acidic than pure water. Something with a pH of 5 is 10 times more acidic than 6, which means it’s 100 times more acidic than pure water (10×10=100).

Trichlor, a popular stabilized chlorine used in outdoor swimming pools, has a pH of 2.8. For easier math, let’s just round it to 3.0. How acidic is 3.0 pH Trichlor compared to 7.0 pH pure water? Let’s figure it out.

(7.0 – 3.0) = 4.0
Logarithmic scale means 10^4, or 10x10x10x10 = 10,000
Trichlor is 10,000x more acidic than pure water.

The role of pH in water chemistry
Managing pH is a critical component of maintaining healthy water chemistry. It is so important because pH is a driving factor in the Langelier Saturation Index (LSI), and also because pH determines how effective chlorine will be. The lower the pH, the stronger chlorine will be. Lower pH means a higher % of the strong form of chlorine, Hypochlorous Acid (HOCl), compared to the weak Hypochlorite Ion (OCl-).

What is Total Alkalinity?
Total alkalinity is a measurement of all alkaline substances dissolved in the water. These substances are primarily bicarbonates, carbonates and hydroxides, and some others (like cyanurate alkalinity). These alkaline substances buffer pH in the water by either taking or giving a hydrogen ion. In other words, total alkalinity is a measurement of the water’s ability to resist change in pH.

Total alkalinity is measured in parts-per-million (ppm), and the ideal range is from 80-120ppm.

The Role of Total Alkalinity in Pool Chemistry
If you’re a pool operator, you probably already know that pH can fluctuate up and down. Another way to think of total alkalinity’s role is that it neutralizes acid.

You could have a ton of 8.3pH Sodium Bicarb floating around in the water, and have the same pH as if you added a smaller amount of 13.0pH soda ash. But the total alkalinity would be higher for the Sodium Bicarb, because there’s simply more of it in the water.

[lovemussb]

Thank god I found you, been looking searching you tube for someone to explain this
But all the videos were 10 mins long, and I still didn’t understand .you told me in 2 mins and I got it.
👍

[dnnbyuj]

It absolutely helped, easy and straight to the point, Thanks

[rhmaster]

Is it poasible that lower alkalinity is possible in higher pH..? I mean 348ppm alkalinity in 11 pH solution... I got this result in a industrial effluent... Is this possible... N if it is... Tell me the reason plz... Thank u..

[boakaif.massaquoi]

Hi.
I worked at a brewery industry as a water treatment technician. A work I am relishing daily since I am new at the profession.

Now here is ny question: I noticed the water pH level for treated water is measuring at 8.6 to 8.9 which I think is too high for soft drinks or beer production. At this point I am always worry and thinking what to do to have a lower pH than what is listed above here. Could you help if you dont mine?

Also, could you provide me with a written explanation for alkalinity and its important in water treatment?

Thank you as I await your answes.

[dland]

So is it fair to say that pH and total alkalinity are two ways of measuring the same thing (how basic the water is)?

[kimberlyr]

Units for alkalinity are q/L or mg/L as CaCO3.

[schmehlchristian]

Hi, here is a funny question... What should I do, when I get my pool water on 6, 9pH and 189ppm alkalinity? True Story. Actually I try to lower the alkalinity by giving some acit to the water. Of course pH degrees to. New values are 6, 4 and 118ppm alkalinity. Now here is the point: what can I do, to raise the pH without the alkalinity? Is there a way? Best greetings!

[owenanderson]

Please advise on the followi g situation: If TA is only a measure of resistance pH change, and the pH is what actually affects the chlorine performance and swimmers' skin, what action should I take (if any) if my TA is way high at around 200ppm, but my pH is a stable 7.2?
I've been considering aerating to raise pH only, to create capacity to add muriatic acid to bring TA down.

[HalfManHalfCichlid]

Great video. I am working on an environmental project and need some input. The EPA alkalinity map for surface waters in the continental US, has many states in the midwest at the top of the scale on the high side for alkalinity. I can find a comparable pH map for surface waters. My question: Would you expect the states with the very high alkalinity to also have a high pH. Any comments would be welcome. Our project has to do with the use of copper sulfate in ecosystems to control weeds and blue green algae. Thank you.

[GAFINNNJ]

PLEASE HELP! I'M IN A RAT RACE.

I have a 30k gal. in ground pool with a liner.
My PH tends to be HIGH as a normal condition.
(except in Winter) I'm always adding muriatic acid to bring it down. (Up to 3 cups / day when it gets hot)

It's impossible for me to raise my TA because, adding Baking Soda to increase my TA causes my PH goes up. Then I'm fighting to get it back down with muriatic acid which brings TA down. This is a real rat race.

Should I bother with TA if the PH in my pool tends to be naturally high?
Is there a more cost effective way of lowering my PH than Muriatic Acid (about $8 / gal?)


FYI My pool has a liner and I always brush the bottom after adding acid so that it stirs up and does not puddle anywhere.

[rbailey]

I bought a water test kit that tests for Total Hardness, Total Chlorine, Alkalinity, pH, Nitrite and Nitrate on a single test strip. The only thing that was not in the ok range was the alkalinity. On a scale of 0 - 240 ppm, it was 0. If alkalinity is too low, shouldn't that have given me a bad pH result? What should I do to verify test results and, if proven correct, what, if anything, should I do to rectify the issue?

[Cruner]

Hi Can you help - I use those test test strips with three items on -Free chlorine, PH and Total Alkalinity. The Ph reads 7.5 the free chlorine goes dark green and off the scale and the Total Alco reads 30ppm when I try to set the Free chlorine to @ 1.5 ppm by diluting the sample I cannot obtain the nice blue colour (1.5) on the strip so what am I doing wrong or is it the test strips that are faulty ?

[andrewwhiteheadmakingmurd]

What if my acid demand test is perfect. But my total alkalinity is higher that 100 ppm

[jua]

I have an interesting situation that I’m not sure if I should modify at this point.

I have spring water to fill my spa. The alklinity is at least 220 (it can move higher. The PH usually begins at 7.2 - 7, 6 depending, but very quickly moves into the 8.2 range after a day or two.

So, I added muriatic acid in 5 or 10oz amounts over several days to reduce the alklinity. It has now stablilzed the PH at 7.6 for 24 hours in still water at a temp of 102º (This is the first time the PH has not crept higher over a 24 hour period.)

But according to a reagent test the alklinity is now 30 (which did not happen until the very last 10oz dose) - which is low. What is the ramification of this alklinity with a stable 7.6 PH ?

Should I jusy leave it?

[somkiatrangkla]

Ph is 6.3, Chlorine is around 3.2 reading of my swimming pool today so what should I do with it. Note, my pool is not a salt chlorinated pool.

[arifrahman]

I've a fish tank (5000 littre). I'm producing fish by Biofloc technology. There i need to maintain the alkalinity. For this purpose, what should i do?

[rainbowlo]

I want to learning more about pool do you have any suggestion for me to take a class
Our hotel is 35000gallon ph is over 10
Alkalinity is 270 l try to put acid to kill HP our pool water so cloudy and not clear
I put 3 bottle caps thio trine
You can teach me please

[castorcastortroiy]

Question. Why my well water PH is low and the Alkaline is extremely high?

[radhakrishan]

Are all (periodic table) anions represent Alkalinity?

[conman]

How do I raise the KH and GH in my fish tanks without increasing the PH?