Is there any way other than using the Pool Calculator, adding chlorine to the pool and seeing the results to find out if my 12.5% is 12.5%? I just started using 12.5% and I know it loses strength quickly, so how do I know it's full strength when I buy it?

It takes some pretty accurate equipment to get an accurate test of strength of the bleach.

You can use the pool calc if the 6% has been pretty accurate in the past. 12.5% should take half as much to raise it the same amount.

Couldn't use the pool calculator to figure the amount to use in a known smaller volume of water, say 5 or 10 gallons, add that amount to figure the strength based on FC rise.

Using the Google-Search field in the very bottom left of the page, search for "test chlorine strength", without the quotes.
Here's the first one:
testing-strength-of-liquid-chlorine-t3165.html

Thanks for the replies. I did a search and surprised I didn't get the thread ohm boy linked. I want to check my supplier to see what I'm getting.
Thanks again.

1/4 teaspoon of 6% bleach in 2 gallons of chlorine-free (and chlorine-demand-free) water is 10 ppm FC. 1/4 teaspoon of 12.5% chlorinating liquid in 2 gallons is 20.4 ppm FC so 1/8th teaspoon is 10.2 ppm FC.

If you have a spare Taylor or TFTestkits bottle from one of the reagents (especially the titrating ones), then they are 24 drops per ml so 24 drops is 1/5th teaspoons. 1/4 teaspoon is about 30 drops. 1/8th teaspoon is around 15 drops.

Thanks again everyone. I'll try it chem geek's way and the method from the link ohm boy posted and compare results. Thanks for the link James but $83.50 for the Taylor Test is a little steep for now.