Could my CYA have dropped? Now 40... that okay? Recommended level?

[bbrock]

Hi TFPers,
Yesterday was full test day. In the on-season, I perform my full testing approx. 1x/mo. At 0745, here were my results:
pH 7.6
FC 5.5
CC 0
TA 60
CH 1100 (yes, I know high, but that is not the topic of this thread. I am managing it and using Pool Math to keep h2o balanced)
CYA 40
water temp = 82

I added 28 oz chlorine (I use 12.5%) and 37 oz MA (I use 14.5%). When my CYA was 50, on the days I added chlorine I would always add to the upper limit of the recommendation. So, I added 28 oz chlorine to bring up my FC to 7.

I am curious how my CYA could have dropped to 40. For approx. a year since I have been managing my water and using the TF-100, it has been 50. I did a partial drain/fill last year around this time to bring it down to 50. FWIW, if it may have affected things, I recently began using a 8 mil solar cover. Is a CYA of 40 okay? I have read so many threads on here that have discussions about different CYA levels. It appears there is no clear cut answer. My pool generally gets sun for approx. 8 hr/day +/-.

Is there a recommended level given my details?

Tx for any help.

 

[jblizzle]

Just wrote this in another thread:

CYA is consumed at a very low rate. Plus losses to splashout and backwashing and rain overflow.
And sometimes over the winter it get converted to ammonia and drops to zero, although usually in a neglected pool.

If you get a lot of intense sun, then up around 50ppm is good, less sun, then lower toward 30ppm is fine.

 

[bbrock]

Tx Jason.

Per the recommended levels page, it appears that 40 is right in the middle of the recommendation for plaster with bleach (http://www.troublefreepool.com/content/134-recommended-levels). Yes, in the summer I get some intense sun for up to 8 h +/-, but again it is only 8 h. Not sure how to quantify "intense" from a temperature perspective or duration.

 

[jblizzle]

If you are losing more FC every day than you like, then raise the CYA level up some. Normal to have to add 2-4ppm of FC every day.