algae and my CYA

[sunofthebeach]

A little info.
My water is Crystal Clear. People often leave my pool with red eyes. I have been fighting algae consistently for 2 seasons in a row and it continues this year. What happens is I am caught off guard see some algae on the walls and test and see that my CL is at 0.
Every season I open my pool to low or no CYA. I have a mesh cover and my pool is a green swamp when I open it. I use bleach until it clears up. I’ve use Stabilized pucks mostly for sanitization with bleach sometimes.
I have a Taylor 2006 test kit and understand the advice of this site.
2 weeks ago I let the pool store test my CYA. They said it was 100. I told them I was surprised, because I always opened it to 0. (They told me that was impossible)
I operated under the assumption I had high CYA and tried to keep my CL up around 8ppm. It is tough to do and I was always surprised how quickly my CL went down to 0 or 1ppm. i have been adding 182oz bottle every night for a week and i still have 0cl the next night. it has been sunny and hot this week.
Last night I tested my CYA with the Taylor test kit. I have had the test kit for 2 seasons and have never used the CYA test. When I tested the CYA, It indicated my CYA was 30.
What is the likely scenario?

1. My cya is 30 and it is ok to use stabilized CL, the pool store test was wrong.
2. My Cya is 100 and my Taylor test kit is old and not giving accurate results.
3. Maybe I have ammonia in my pool and that is why my CL is not as effective and I am fighting algae.



PH 7.4
AL 90
CA 180
CYA 30 or 100
Gunite pool, DE filter, no heater 23,000 gal

[madwil]

Wouldn't trust the pool store numbers- I'd bet your CYA is 30ish...
to get a good idea, you need to test the FC 1 hour after adding, then see how much it drops.
I'd add enough bleach to get FC to 5, test in 1 hour to confirm, then test again the next night; if it drops to 2-3, CYA 30 is probably right. If 0, no CYA. If 4-5, 100 CYA...
just a very rough guide- I think 50ppm CYA still loses 50% in a full sunlight day!

[kelemvor]

Is it your FC or CC or both that are zero? I'd think if you had algae the FC would be converted to CC pretty quickly until the algae was all dead.

[madwil]

if you do have ammonia, it will almost instantly convert FC to CC; this could be why eyes are irritated/red!
and the pool store is mistaken about impossible- it is very possible to lose all your CYA while the pool "hibernates"; which would also be a source of ammonia, and would eat your chlorine until you clear it out...

[CarlD]

CYA is by far the toughest test to run.

Do you:
1) shake the mix of pool water and reagent for at least 30 seconds?
2) Stand facing the sun?
3) Hold the measuring tube at waste level and SLOWLY add the mix till the dot disappears?
4) Dump the mix back into the vial and run the test a second time with the same mix?
5) Perform the test the same way every time?

If you do this, then your measure is accurate and theirs is not to be relied on.

I speculate that your CYA only got to 30 recently and you've been battling chlorine breakdown until then.

I would shock the pool to 15ppm and keep it there for a couple of days, and see if it mostly holds. If it keeps dropping, especially overnight, you are still fighting something and need to maintain shock levels until then.

Carl