adjust cya before or after shocking

If I can't get light out of pool, is super shocking all for naught???

Help! On 5/30 at 9pm, I figured out that I had mustard algae...thanks to you guys and I went ahead and added several qts. of bleach that evening to start usual shock process planning to go to mustard shock after that, per website instructions. On 5/31 at 7:30 am, FC = 22.5 and I thought the CYA = 65 so I understood shock to be 20. I kept FC over 20 on 5/31 until I tested at 7:30 pm and FC was 16.5 I kept FC > 20 on 6/1 and lost 2.5 ppm of FC overnight and was at 19 at 7:30 am on 6/2. Got FB back over 20 on 6/2 but lost 2 ppm overnight so FC = 18.5 at 7:15 am on 6/3. Got FC > 20 all day on 6/3 but lost 2.5 ppm overnight again. This morning, at 6:30 am. FC = 22. I decided I needed to recheck CYA this morning, and it now looks to be 50. I had just added CYA (through sock) on 5/31 and got the higher reading.
So, does CYA settle down after being added? Why do I keep losing > 1 ppm of FC overnight? I was hoping to move to mustard shock today but guess I'm not done with regular shock yet. Please advise. Thanks!

CYA doesn't settle, you usually lose it by splashout or backwash. A drop of 65 to 50 may just be the accuracy of the test.

Quote:

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Originally Posted by BigDave

CYA doesn't settle, you usually lose it by splashout or backwash. A drop of 65 to 50 may just be the accuracy of the test.

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In other words, by dilution. But try to always run the CYA test the same way. One trick I use is to pour it back into the squeeze bottle and run it again (it doesn't change the solution to do this). Sometimes I do it three times, always trying to do it the same way. This helps me neutralize errors in any one of the readings, and I'm not using any more reagent, just reusing the sample.

Katey,

This thread has gotten VERY long and hard to keep up with. Could you please enter your pool info here:

Pool Chart Entry Form
Pool Chart Results

. . . and log your test results, here:

Pool History Entry Form
Pool History Logsheet

That would make it MUCH easier to keep up with what's going on, and give an intelligent response. I'm going to go back and put in the first couple of test results you have, but if you'd do the rest, and any new ones. The short URL for your test results is http://goo.gl/6ok5j and I'm adding that to your signature.

Thanks!

I'll have to do this later/this evening as I'm at work today. thanks.

I entered everything except today's.

If you would, test EVERYTHING except CYA, and post complete test results INCLUDING calcium hardness, but using the CYA levels you got earlier today. Also record salt and filter info.

I just tested and added results except for cya. tried to go back and add results from yesterday but couldn't. I turned on SWCG this am at 50% awaiting mustard algae shock guidance. Looks like I need to lower TA but will wait to hear from you.
Appreciate the CYA testing tip!
Thanks.