CYA increasing faster than possible...

[Themadczar]

Before replacing the water in my pool: tested cya at 0 after opening (water didn't turn cloudy at all). Attempted to treat pool for ammonia/nitrates chlorine demand. But before that was properly diagnosed, i had added 5# of dichlor. For my 13200 gallon pool, that should amount to cya at 23 ppm. Tested it slightly over 40.
After replacing the water in my pool: no cya since it was fresh water from the city. Over the last week (completed the refill a week ago yesterday) i have added 6# of dichlor. A couple days after adding the fifth, I tested cya at 40 (it should have been 23). I added another pound last night. By dead reckoning, I should now be at 28. I took a sample to the pool store to test my salt level (I'm considering adding salt for comfort as discussed in other posts, but I needed to know my starting level and I don't have the salt test kit). The pool guy did the drop test for cya (NOT the computer) and came up with 50ppm! How am I repeatedly getting a near double dose of cya from dichlor? It's the stuff from Sams Club, and the only other chlorine I add is bleach (which I have yet to do since the refill). And if it can take a week for cya to show up in a test, my cya could theoretically be higher thean 50. The only things I have put in my pool (besides people and pool toys) since the refill are 6# of dichlor, 2 cups of borax last Monday (fill water had ph of 7.0), and about 3 quarts of muriatic acid over the last week to lower ph due to co2 outgassing from very high ta fill water. Needless to say, I'm not adding any more dichlor for now... Back to bleach. I would simply like to know how this is possible... The numbers don't add up.

[chem geek]

When you are doing the CYA test are you standing with your back to the sun holding the tube in front of you looking down into it? You want strong indirect lighting. If you have the tube directly in the sun, you will read lower than the actual amount while if you read it in indoor lighting (unless very bright indirect) then you will read higher than the actual amount. See this link for some photos of the black dot disappearing. You can get 50 ppm CYA standardized solution if you want to experiment with your testing technique.

[Themadczar]

Ok, I will try the test in indirect daylight... Thanks for that; I was unaware.

[Themadczar]

Tested today in indirect sunlight... Made all the difference. Cya was a little ess than 30, which is right where it should be for the amount of dichlor I added. I had no idea lighting would make that ig a difference. Thanks, chem geek!