Isn't 12% chlorine 88% NOT chlorine?

[BmerMeUp]

Hello, TFP peeps! Long time lurker here with a question regarding chlorine math!
I did try to find the answer by continuing to lurk but the particulars are very specific and I struggled with search terms which would successfully extract this content from every other post on the forum.

So:
Let's arbitrarily take a 20,000 gal pool. Measuring in "parts per million," we get:
20,000 / 1,000,000 = 0.2 gal = 25.6 oz = 1 ppm.

So "1 ppm" of "anything" in this pool is 0.2 gal (25.6 oz) of that substance.

Logic would then suggest, to raise the chlorine content of this hypothetical pool from "x" ppm to "x+1" ppm, I need 25.6 oz of chlorine. The pool calculator sort of agrees, but that's where the subject line confuses me - 6% vs. 12% vs. 100% chlorine. Unless... when we say "+1 ppm of chlorine" we actually mean "+1 ppm of [12%] chlorine (plus 1 ppm of 88% more water... )"?

Pool calculator says:
To go from X to X+1 ppm FC, add 41 oz of 6% "bleach" or 21 oz of 12%.
(somewhere around 9.7% bleach will give me the 25.6 oz mathematical target)

So I guess that's my question - when we say "ppm chlorine" in relation to FC, it would seem we actually mean "ppm [~12%] chlorine"?
True / False?
Thanks!

 

[jblizzle]

False. We mean 1 ppm of FC. Does not matter the source of the chlorine. Is there a reason you doubt the calculator?

Welcome to TFP!

 

[sargent]

Well your math is wrong to begin with. One millionth of 20,000 gallons is 2.56 ounces not 25.6 ounces. Divide 2.56 by 0.12 (if you are using 12% chlorine), and you wind up with 21 ounces of liquid chlorine. When you want to add 1 ppm, the amount will differ depending on the concentration of the chlorine.

 

[BmerMeUp]

Oops. Yes - 0.02 gal not 0.2 gal. Ok, got that. Missed a zero somewhere!

I see now the part I was missing in the math as well - coincidentally being off by 10 (missing a zero) gave me 25.6 vs. 21 which made me think they were related; if I had properly calculated 2.56oz I would have better known I was still missing a step completely. Dividing 2.56 by 0.12 was entirely missing and now makes sense for the 21oz reply from the calculator! Thanks!

And for jblizzle - Hi. No, I have every confidence in the calculator, in fact it is quite brilliant. I was trying to understand what it was telling me, and the difference between the various %'s of chlorine available and how that affects the results. I am currently waiting for delivery of a chlorine pump and am trying to properly understand my options, i.e. if I need "x"ppm of extra chlorine, how much at 6% and how much at 12% would that be and why. The math (and math correction) from sargent helped fix that.

Next step - get a reliable tester kit (in Canada... boo) and start tracking my chlorine consumption so I know how much to add!
Thanks guys!

 

[jblizzle]

Well, you would need twice as much 6% as 12% for the same ppm rise

Yeah, you guys up north are kind of limited in your test options