What depletes CYA?

[keep-it-simple]

My test kit came in Saturday. (Baaaaad idea y'all for me to have test kits. I want to test everything every day multiple times a day just to see what's going on!!)

First test 4/13
FC - 0
TC - 1
pH - 8.0
TA - 130
CH - 120
CYA - 0
Salt - 2320

I added:
5lbs trichlor
10lbs stabilizer (CYA)
1 quart muratic acid
8x 40lb bags of salt
And turned the return jets upward to aerate
(Turned the swg off to let salt dissolve)
(I added the CYA in a pair of pantyhose and hung it in front of a return jet. It was completely dissolve from the pantyhose within about 24 hours. )

Second test 4/15
FC - 5
TC - 5
pH - 7.4
TA - 100
CH - 120
CYA - 40
Salt - 3800

So now I'll turn the swg on maybe 20% and monitor TC
Pool calculator is telling me 6 more lbs of CYA to get to 70. At $20 per 5 pounds this stuff is expensive and I'm hoping to not have to add it often!
What causes CYA to deplete and how often should I expect to have to add it?

 

[keep-it-simple]

I haven't tested my fill water yet. More tests to run!

 

[brg88tx]

most everyone on this board says only water replacement lowers cya, but I have found in my pool that hypochlorite in bleach and cal-hypo oxidizes and lowers cya to the tune of about 5-10 ppm per month.

 

[JasonLion]

Most people only need to add CYA once per season.

Oxidation of CYA can happen but it is much slower than that, perhaps 2 ppm/month. Mostly CYA is lost when you replace water, for example when you backwash or winterize, and occasionally CYA will vanish over the winter.

 

[bigmoguls]

I'd give you some of my CYA, but it's all in the water :0

 

[imwarren]

Wait before you add more cya yer I recall even if disolved it can take several days to register on test

 

[linen]

Wait before you add more cya yer I recall even if disolved it can take several days to register on test

This is a good point by imwarren. Adding 10 lbs to your 24000 gallon pool should raise it up 50 ppm. It can take up to a week for cya to show up. In addition, there are a couple of reasons to wait to add more, one is knowing your pool volume accurately, and two, there may have been a small amount of cya in the pool even though you read 0 (unless you just refilled the pool or know the full history of the water). I would wait to add more until ~6 days go by and test again.

 

[keep-it-simple]

Okay. Thanks, y'all.
So should I add muratic acid to lower the pH in order to keep working on TA for now?

 

[linen]

If you are still at 7.4, I would continue to aerate up to 7.8, then drop it back down.

 

[keep-it-simple]

Edited my sig. Measured pool depth. I had estimated 7' deep end but it's 8'. I measured the step depth too and calculated it all in pentair volume calculator.

Just tested fill water.
TC - 0 (good)
pH - 7.2
TA - 140
I didn't test CH since my pool is fine on CH an a wide range is acceptable.
I didn't test CYA because tap water shouldn't have any...
So hopefully the kids can splash out any extra TA over the summer as we refill the pool!