"bent" wrote in message
...
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.


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It's been a long time but I seem to remember that Total Alkalinity was
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