How to test the liquid shock from pool store for it's available chlorine

Basically, I need to know exactly how to use my FAS-DPD kit to test the Malibu Pool Shock (liquid chlorine 12.5%) itself. I'm suspicious that it is not 12.5% but much, much less.

In 6 straight days we've added enough each evening to bring our FC to shock levels of 28ppm. Starting FC was 9.0-12.0 and CC was 1.0 - 1.5.

Two of the seven applications yielded 16ppm FC an hour after adding it and the other five times it yielded 11.0 - 13.5 ppm. We lost 1 ppm FC or less by sunrise each time and the CC never changed.

Last night we added 3 gallons (128oz each of 12.5%) to an 18,000 gallon pool that had these readings before adding:

FC of 9.0
CC of 1.0
pH of 7.6 or 7.8
TA 120 or 150 before correction
CYA of 60 or 70
Pool water absolutely clear and still being aerated to keep pH from falling.

It yielded only 16 ppm one hour later so we added 2 more gallons at 10:00 pm.

This morning the FC was 12.5 and CC was 2.0, up for the first time in 6 days. Scratching my head - it has to be the pool shock.

How can I accurately determine what the strength of the pool shock we are buying really is?

I test the LC I buy every now and then using the following dilutions and test method:

* add 10 ml LC to 1 L water, mix,
* add 10 ml of the mix to 1 L water, mix
* test using the 25 ml procedure multiplying the # of drops by 0.2.

Mine tests out at between 10 and 11%

You can determine your source strength - someone ( I think CarlD ) has a thread on it somewhere on the forum - you're a subscriber so you can search.
I don't really see why it matters. You need lots of FC as demonstrated by the fact that you have persistent CC readings: FC is being consumed reducing (oxidising) suff in your pool and showing up as CC.

Shock level for your CYA is 20, so add the dose of bleach you think you need, pump on 24/7, let it mix for an hour, measure FC if it's not above shock level, add more and adjust your dosing as necessary.

BBB for clearing a mess:
Bleach - Bleach - Bleach and Brush - Brush - Brush.

Thank you Anna and Big Dave!

I followed Anna's instructions and mine tested 12.6%, right on the money. It was also the first time I've felt confident with the "reading" of the results after using the K2006, which brings up other questions on my troubles interpreting the results when using it on our pool water. I'll post those questions in this thread next, but.....

I have other questions regarding exactly what to do with our pool right now to ensure it's ready to swim in by this weekend. Which thread should I post further questions about getting rid of my CC ...."Testing and Adjusting Pool Water Chemistry" or "Pool Chemicals & Pool Water Problems"?

This thread has run it's course since you were able to achieve results.

Post about your CC problems in "Dealing with algae" and post questions about using the test kit and evaluating readings in "DPD-FAS based testing".

I'm adding a tag to this particular thread, 'dilution chemistry'.

Thanks!! :)