Keep your chlorine level at 15

Please help me understand.Im not sure when this forum says keep chlorine at the level of 15 shock level.Question how do you know when it is at the shock level.when I take my daily chlorine this only goes to 5 and the BR Side 10

I am running out of the DPD POWER that I test for cc,I use the bleach cal and have put chlorine in as stated.but water is still a little cloudy.I just need to know when to tell if im at the shock level.
Also where can you get DPD POWER

THANKS

The chlorine level you need to shock your pool depends on your CYA level. In the Chlorine Thread on this forum, you will find Ben's Best Guess chart - that will give you the recommended chlorine levels based on CYA.

If you mean the FAS-DPD powder, then I believe Ben sells refills on the poolsolutions site. The FAS-DPD test will give you a free chlorine (FC) reading which is pretty accurate. If you want to measure higher than 5 ppm with the OTO test, you can dilute the pool water sample with two parts distilled water and multiply your result by 3. This will not be as accurate as the FAS-DPD test but it's better than nothing.

Peter