OK,

What is Total Alkalinity?
Total Alkalinity is actually a bit of misnomer for anyone who remembers anything at all about high school chemistry. We think of Acidic as low pH and Alkaline as high pH. Total Alkalinity doesn't refer to that--as I said it's a bit of a misnomer.

Richard (Chem_Geek) can give you a far more precise definition, but in short T/A is a measure of the BUFFERING of pH.

That means it helps keep your pH stable, so it isn't constantly changing. The accepted normal range is 80 to 125ppm. For concrete/plaster/tile pools it's very important to keep your T/A in this range. For vinyl pools you usually won't have a problem unless you hit 200ppm AND you have a high hardness level (you don't). So it's not a big worry for us vinyl boys and girls.

Richard has challenged some of our assumptions that higher T/A in the range is better and has shown that the 80-90 range can give better buffering. That's all very technical.

But, unless you are having a problem with oscillating high and low pH levels at your T/A of 175, you simply don't have a problem with your T/A.

Where is pH dangerous to a vinyl pool?
Normally we worry about pH reading below 6.9 for vinyl pools. For concrete/plaster/tile pools, much lower pH levels can be safely tolerated without damage to the surface (I'm not expert on those).

The problem is a lot of test kits either have 6.9 or 6.8 (usually 6.8) as their lowest measured level and they don't have a fine enough differentiation for you to see if it's 6.9, 6.8 or even a little below. That's why we worry if it shows anything below 7.0--because at 7.0 we know we are in the safe range.

Low pH will soften and weaken the vinyl. Extremely low pH (like using the hideous "slug method" to lower T/A) can actually dissolve the vinyl--new wrinkling at the point where the muriatic acid was added is a warning sign.

Aeration to Lower T/A
Again, a misnomer. The process as originally described by Ben was very confusing but it's actually quite simple.

1) T/A measured levels go up and down as pH goes up and down--it's not actually that the T/A is changing, though we want to do that. If you add acid to lower T/A then add Borax to raise the pH back it will seem that you are not getting anywhere.

2) So we have to be able to raise pH and NOT have the T/A rise with it. Aeration does that. Again, without getting into the chemistry, the aeration allows certain components in the water to create a less acid and more basic solution.

3) The process is:
a) Lower pH to 7.0 by adding acid
b) aerate to raise pH back to 7.4-7.6
c) Measure T/A.
d) If T/A is not at the desired level, repeat a), b) and c) until it is...this is the "rachet" method.

4) Aeration can be splashing 12 year old boys, a fountain, or just leaving the pool uncovered and pointing the return toward the surface so the water is agitated.

That's it. I hope I helped.