What chlorine level to shock -- now that half my CYA is gone

[JimK]

I added five 121 oz jugs of 8.5% bleach around 7:30pm (it's been raining today so no sun) and brushed the entire pool. I just checked CL level (9pm) and it barely registered! This is what it measured:

FC < .5
CC < .5

Strange......... The water is cold (about 60); does this impact the DPD Powder test?

Does this mean I'm fighting ammonia? Should I go ahead and add the other 5 jugs tonight, or wait until morning?

PS -Just found this in a Google search:

"...11. When a DPD chlorine test flashes a little pink then turns crystal clear, your water has almost no chlorine in it.
The opposite is true! More spas are fried and bathing suits bleached because of this error than just about any other. As you know, the universally accepted DPD test for chlorine turns progressively more pink as higher residuals are encountered in the sample… that is until the indicator is itself reverts to a clear resultant. This phenomenon occurs somewhere near 20 ppm chlorine, the actual value varying with different pH or total alkalinity conditions. Many, many untrained operators or “helpers” have dumped excessive amounts of chlorine in their water (most often in hot whirlpools or spas), thinking all along that for some crazy reason they just hadn’t yet put enough in to get a reading! In a small body of water this testing error has resulted in a few hundred parts per million chlorine residual, creating some very unsafe, damaging or at least unpleasant conditions..."

I didn't notice it "flash pink", but I'm wondering if the CL level is over 20 causing a reading error? Out of curiosity, I did another sample and added several scoops of powder (maybe 4 to a 10mil sample?) but that didn't seem to change anything.

Thoughts?

PPS - Found on Taylor site where FAS DPD test can measure up to 20ppm. Hmmmm.... I have a hard time imagining all that chlorine was gobbled up in 1.5 hrs....I'm thinking CL may be higher than 20ppm so I'm not getting a good reading. I'll hold off adding more CL tonight and check it again in the morning.