This spring I opened up the pool to perfection. Numbers were perfect, water was clear, etc. The CYA was right where it was when I closed last fall....at 45. After my initial test, I didn't check the CYA again, because it never reallly changes much. However, my pool care had become a little sporadic, and I should have realized that after I added my initial 10" of water to top off the pool from the winter, my CYA would drop some.
A couple of times during the last month, my FC dropped to about zero, but after adding more chlorine, my CC still seemed to be less than 1.0. so I never worried much about it. After all, the water was still clear.
I recently had to go out of country, and knowing it was going to be very warm, and the family would want to swim, I instructed a family member how to run stuff, and told them just to add some chlorine every day until I got back, and then I would fine tune it.
Well, long story short, a couple of days after I got back, I checked the pool, and to my horror, I had green alae growing all over the bottom. I should have checked all my numbers at that time, but I panicked, and began dumping in chlorine to bring to shock level, and spent the rest of the evening brushing and sweeping.
For the last 4-5 days, I have kept the pool at shock level, brushing every day, and have been doing an OCLT every night. My last test I went from 18 FC in the evening, to 16.5 the next morning. Last evening after work, when my levels had finally come down to acceptable FC ranges, I went ahead and did a full test.
The results were:
FC - 6.5
CC - 1.0
PH - 7.5
TA - 140
CYA - less the 30, once the tube was full, I could still see the black dot pretty clear. I'm guessing maybe 20?
I checked the CYA 4 different times, in different lighting, and it always was the same. I tested it with cold water, I tested it with room temperature water, I used different reagent tubes....always the same.
I'm thinking that perhaps the low CYA is the reason I have been struggling to maintain acceptable FC levels (My neglect not withstanding!)
But here's my question: Before I go adding more CYA and create another issue, why would it be so low? I know I added about 15% water, and there has been a normal amount of rain, but should it have dropped to under half what it was the first of May? Due to a high CYA level last spring, and a partial dump/refill, I had bought all new R-0013 last year, so this stuff is no more than a year old, and it appeared to be consistent when I checked it in May.
Is there something I'm missing here??
Edit: And if the CYA really is that low, I've been shocking the pool with a whole lot more chlorine than needed!
Thanks for the input!