50% CYA gone after AA treatment, and the FC all gone after one day of sunlight
Finally, I have tried AA treatment this weekend.
My pool has some light stain on its floor. I tried Vitamin-C, it worked pretty well, so I decided to get some AA.
Last weekend, I added 1 and half bottle of Pink Stuff and lowered the pH to 7.2, with hope that the stains would lighten without AA. No obvious improvement after one week.
So, I lowered the FC to 0, added polyquat 60, and added AA (2lb for my 15000 gal pool).
Before adding AA, I found the pH was about 7.6, but I thought the AA would bring down pH, so I didn't add acid to lower pH to 7.2 before AA. After adding AA and another half bottle of Pink Stuff, the pH was still about 7.3ish, so I added MA to bring it down to 7.1. Left filter run for 24 hours.
I was really disappointed to find out that the stains were still there (although a little bit lightened) this morning... I decided to live with it...
I started to bring up FC and TA. The pH was 7.3, so I added some MA.
However, I have noticed that the CYA was much lower than last weekend. From 40 dropped to less than 30.
I don't know what happened. There wasn't large amount of water replacement, not backwash during last week.
Could anyone please tell me the reason of my AA treatment failure? Was that because pH was not low enough before adding AA? (this was not mentioned in the instruction... I kept pH<7.2 after adding AA)
Why my CYA drops after AA treatment?
Here are the numbers before/during AA treatment:
FC = 0;
CC = 0;
TA = 70;
CH = 250;
CYA =40 (before AA), <30 (after AA)
pH = 7.6 (before AA), 7.1 (during AA), 7.3 (after AA 24 hours)
Another thing is that it didn't take much bleach to bring FC back to 3ppm (I added the amount of bleach for 4ppm in total according to poolcalculator) The overnight loss is 0.5 FC.
However, FC doesn't survive sunlight of next day! All gone...
Does anyone know the reason for CYA all gone after only 2 days?