Why do (pool) water test strips have both a pH and Alkalinity Low to High scale?

Ok, anybody want to attempt to splain to me why there is both a "pH" (6.2-8.4) and a "Total Alkalinity" (0-240 ppm) scale on a pool water chemical test strip kit . I have been using the strips that have the 4 square foam pads on the ~1/4" x 4" plastic strip that you dip in the water, wait and then compare the colours change on the pads to the reference colours on the label of the strips' bottle. The strips have a colour range for Total Bromine (0-20 ppm), Free Chlorine (0-10 ppm), pH, and Alkalinity. Granted, it is likely that the strips I currently have are technically past the expiration date, and I will get some new ones soon, but firstly just to compare the results of the test between the old strips and new strips, so I cna finish them off. Any comments on how off they can get with age?
This is my problem - ngQ(uestion):
I was taut in skool that pH and alkalinity was the same scale. The number is determined from the definition regarding the hydronium ion concentration, and math or something like that. The pH of neutral water is about 7. That it, it is neither acidic nor base in its chemical character. If the number is low, like 3, it is "acidic" and if its high, like 9, it is alkaline (base). But if it is acidic (low number on the pH scale), by definiton it CANNOT be alkaline at the same time, or vice versa: it cannot be alkaline and be acidic too.
So why are there two scales on these (pool) water test strips, which read from low to high for both pH and Alkaline? There is a pH and a Alkaline scale!? So according to the pool companies you can have a low pH and a low alkaline pool at the same time, or high & high, or low & high, or high & low.
Because I go to the chemical cupboard for the right chemical to fix the problem (assuming all other parameters are being considerately moderated too) and I find chemicals labelled "pH Up", "pH Down", "Alkalinity Up", and "Alkalinity Down"! And I don't want to do anything, (a) because the strips may be wrong (via expiration) or (b) the pool chemical companies may be full of crud.
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

http://www.poolcenter.com/watbal.htm -----
- gpsman
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bent wrote: ...

Overall, yes, but regardless of the pH there are still both types of ions present; simply in differing ratios.
The other poster's link gives a reasonable explanation of why the testing is done for both in a pool altho under the Alkalinity section there's some real voodoo "chemistry"...
"... High levels of alkalinity are lowered by the addition of an acid (similar to pH). Experts recommend "pooling" the acid in a small area of low current for a greater effect on alkalinity. That is, adding an acid will lower both pH and alkalinity. Walking the acid around the pool in a highly distributed manner is said to have a greater effect lowering the pH than the alkalinity. Pooling the acid has the opposite effect. ..."
That's a load of hooey for sure--pooling acid (or any other additive) will have an disproportionate effect locally, but can have no effect on the bulk properties--the same amount of acid or base will have the same effect on the total average properties once the water is thoroughly mixed as if it were distributed initially.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
bent wrote:

In poolspeak, Total Alkalinity (TA) refers to the concentration of sodium bicarbonate. See rant below.
What you're remembering from chemistry class is pH versus pOH. Those are scales for measuring acid / base. To simplify, pH is the concentration of the hydrogen ion (H+), and pOH is the concentration of the hydroxyl ion (OH-). They're complementary:
pH - 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pOH - 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Rant: Non-technical people keep making up terms that conflict with scientific definitions. My least favorite is "natural", which in strict terms means "obeying the laws of nature". That makes it a totally useless definition, since anything which doesn't obey the laws of nature doesn't exist.
--
Steve Bell
New Life Home Improvement
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
SteveB wrote:

See the spate of articles today on gay marriage in California.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
from http://www.poolcenter.com/watbal.htm
under the pH text: "To have pH in balance we adjust the water with additions of pH increasers (bases) or pH de-creasers (acids) to achieve the range of 7.2 - 7.8. If ....pH value below 7.2 ... you will need to add a base to ....[if] above 7.8, ....add an acid"
& under the TA text: "Low alkalinity is raised by the addition of a base (similar to pH); sodium bicarbonate is commonly used. High levels of alkalinity are lowered by the addition of an acid (similar to pH)."
So to fix my low pH and low TA according to the poolcenter's (above) text
to fix low pH : add a base to fix low TA : add a base
That is just deduced from their text
Sodium Bicarbonate is the recommended base, to raise a low TA, under the poolcenter's TA text. I have two different brands of "pH Up/Boost" chemicals and they are both "sodium carbonate".
But I have no chemical labelled for TA Up/Boost. Is it the same one? [The Na-C?] So seriously, at this point, I'd just be happy with like a solution to the current problem! Hello.
I do have a chemical labelled for pH down, which is "acid sulphate of soda" which says "to lower pH and alkalinity of swimming pool water".
p.s. I have three different brands of test strips here & all three have both pH and TA scales.
I thought I had a point to this, and I had the evidence, but all I can tell you now is that I don't think I can remember my name! So if high is high add low. And If low is high add low. No, what? Am I high?
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think I now have also another logical legitimate good question, too, stemming from this. If the pH and TA responded the same to the same chemical additions under the same conditions so far: does that mean that the chemical for fixing a high pH and the chemical for fixing a high TA woud be the same?
Oh, wait I just wrote this didn't I: "I do have a chemical labelled for pH down, which is "acid sulphate of soda" which says "to lower pH and alkalinity of swimming pool water"."
So there are only 2 chemicals for the four possible problems of: pH low pH high TA low TA high ?
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

something that built up over time as you kept adding chemicals to adjust the PH one way or another. At that time I think Total Alkalinity was something you wanted to stay as low as possible and when it got too high you had to drain some water and replace it with fresh water.
Of course, I could be all wet. ;>)
Don Young
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don Young wrote:

pH is a measure of the hydrogen ion concentration (lower number is more acid and more hydrogen ions). Total Akalinity is a measure of the amount of acid you have to add to lower the pH.
In very pure water, only a little bit of acid (or a little bit of some alkali, such as sodium carbonate) will cause dramatic changes in pH.
In water with years of pool chemical residues, it can take much more pH adjustment chemicals to make much of a difference. Such solutions might be described as highly buffered.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

yes...
I look at it this way... if you have say 1 gallon of water and say 10 grams of acid and 10 grams of base, the pH is neutral and the total alkaliinty is low...
but instead if you have 10 pounds of acid and 10 ponds of base, ( I exagerate here) the pH is still balanced but the total alkalinity will be high.
Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Interesting chemistry you're using there. If you mix a base and an acid together until you get a neutral pH, you don't have a high alkalinity or a high acidity. What you have is a salt solution.
A glass of hydrochloric would rather nasty to drink. A glass of sodium hydroxide solution would also be rather nasty to drink. Mix them together until you get a pH of 7 and what you'll have is simply a glass of water with salt disolved in it. Not the tastiest thing in the world to drink, but not nearly as bad as either of the original 2 ingredients.
And yes, mixing a base and an acid will always get you a salt. The type of base or acid you use will determine what salt is produced. And not all salts are as benign as good old sodium cloride, but they're still just a salt.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
http://www.lamotte.com/pages/pool/handbook/chapter3.html
For those who thought the details were a little out of grasp (like me) this is a pretty good one-stop explanation, having read through a few different sites for a search detail "is bromine a stabiliozer ?": no bromine is a spa oxidizer/sanitizer suitable more for spas, whereas Chlorine is more for pools, I think
-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.