So I opened my pool a few weeks ago. Weather has been awful and no one has even swam in the pool yet (my ladder isn't even installed yet). Weather has only been in the 60's to 70's with a lot of rain and overcast days. Tested my CYA and it was below the readable level in the tube (I have the CYA test from TF Test Kits I bought last season as my reagent ran out last year). So I assumed a level of 10 and added 100% Cyanuric Acid (Omni branded Chlorine Stabilizer granules that I purchased new in April 2011) to bring it up to a target level of 35 (used pool calculator). I added the granules to 2 panty hose and hung them in front of my return jet. Ran the pump continuous for 24 hours and then set it back to timer mode (2 hours on, 4hours off for a total of 8 hours of "on time" per day). The CYA was out of the panty hose after a few hours. I did not backwash the filter until one week later (prior to CYA test #2).
One week later (last Saturday) I test the CYA again and again it's below the readable level! At the top of the tube the mixture was starting to look cloudy as if the dot would disappear with a little more solution, so I assumed a level of 15 and raised it to a level of 34 (that was all the CYA I had left in the bottle).
My questions: 1) Shouldn't I have read at least 25 at my second test even if I was 0 during the first test? 2) Is Cyanuric Acid (granular) something that loses strength and should be bought fresh each year? Could it be that mine has lost it's potency? It has always been stores in the original bottle out of the sun inside a shed (and in my basement this past winter).
I do feel confident in my testing procedure as far as mixing appropriate amounts of pool water and reagent go and mixing properly (shaking vigorously, waiting min. 30 secs, shaking vigorously again). My chlorine depletion has been much faster than I have expected (especially with the nasty weather we've been having) so that seems to indicate that my CYA is much lower than it should be. I've been seeing it drop 5 to 6ppm per day! I did suspect that perhaps my liquid chlorine had lost some potency, but testing a few hours after adding shows a reading near what I expect. One thing I don't like is that I can't test CYA again for another week! And I'm learning that I can't just assume the CYA is at my target level!