Why can't I get my CYA up

[Deb04]

For the fourth summer in a row, the entire time we've had our pool, I'm having trouble getting the CYA up. I added four lbs of Cya last week and, while the ph dropped exactly as expected, the. Cya didnt move a speck. I'm going to add another 4 lbs. Every year I go through this, adding more cya and it inching up very slowly. By the end if the summer I maybe get cya to 50 and then it's time to close. In the spring cya is almost all gone.

Any idea of cause? I know I could be underestimating my water, but not to the point of NO cya rise. Pool is 18 by 36, kidney shape with a bump on the side, shallow end is 3 ft, deep is 8 ft I doubt it is converting to ammonia because my FC looks good.

FC 4.5
CC. 0
PH. 7.3
CH. 140
TA. 80

Thanks.

 

[aa62579]

With a SWG, I believe you want a higher CYA.

If I plug in your numbers to the pool calculator, to get to a CYA of 70, if you started out at 0, would take 11 pounds.
The 4 pounds you added would raise you about 25.
If you add the other 8 pounds, it would get you up to around 50, if CYA were 0.

A week after you have added the 8 pounds total, retest, and we can go from there.
BTW, how are you getting your test results?

 

[Butterfly]

First, sometimes CYA just disappears during the winter - without ill effects/side effects.

If you had zero CYA and added enough to get to about 25, assume it is in the pool. However, the tester won't measure below 20 and it's quite a subjective test. So, even if it were all dissolved, there's a chance you wouldn't be able to tell. The test is also +/- 10 ppm or so.

I agree with aa62579 and suggest you add enough to get to 50, wait a week or so to confirm, then add the balance needed to get to the ideal limit for a SWG.