Where'd my CYA go?

[adeller]

I'm at a loss. Requesting help from the experts here.

I have been running my pool for 2 1/2 years now. I have had issues with low Cl this year. Just replaced the salt cell a couple months ago. A few weeks ago I had begun a SLAM process due to high Cl demand. At that time I tested the CYA to get the shock value. It was 40, low, but I didn't see the need to raise it before entering the SLAM process due to advice I have seen here. Had to end prematurely due to a weekend out of town, and it was taking longer than I thought it would. After limping along through a couple of pool parties I am now entering the SLAM process again. I am not quite holding a Cl level with the SWG set on 80% (Digital Nano), which is way too high.

So, I tested the CYA yesterday to get the initial value for the Cl. And.......0, yes 0. I know it was night, but the sample was completely clear. My reagent is < 1 year old and having talked to our very knowledgeable TF100 supplier, this is one of the more stable reagents. I have had problems with the CYA slowly sliding down in the past, but nothing like this. So, now the troubleshooting:

1. It is not a leak (been there, done that) If it was, doubtful it would have gone that low that fast anyway, and I am not adding anywhere near that kind of water.
2. Test operation. I have repeated the test, same result.

I added what I had yesterday and got more today.

What in the world could destroy the CYA like that? Or what am I missing?

The water is clear, always has been.
Cl - 22 (I wanted to make sure it was still above shock value when I got home due to the low CYA level)
CC - 1
CYA - 0
Salt ~ 4000 (I know it is high)
TA - not current

Ideas?

Thanks in advance for any help.

 

[svenpup]

The only ways you can lose CYA like you are describing is water replacement or bacteria consuming it when FC goes to zero. The only way water replacement could do it without your knowledge is a leak and an autofill. If it's the bacteria version it is frequently associated with ammonia. Ammonia can be tested with a cheap test from a pet store or can be inferred if you have huge FC demand and get huge CC.

 

[kcindc]

First, I would retest your CYA during the day just to verify your results.

Second, please do a full test of results and post (we also like to see PH, CH, TA).

Typically a quick disappearance of CYA means ammonia conversion and that doesn't appear to be happening because your CCs aren't high enough and your FC isn't disappearing instantly. CYA does degrade in a pool, but is a slow degradation over a long period of time. When was the last time you added CYA to your pool?

Do you have an autofill?
What size is your SWG?
What % setting is your SWG? How long do you run it a day?

What is your CYA testing history (ie May 1 CYA=X, June 15 CYA=X)?

 

[adeller]

KCINDC,

When was the last time you added CYA to your pool? Not exactly sure, it has been at least several months.

Do you have an autofill? Yes, but it is off. I am filling manually, which is why I know I am not adding much water. Only have to raise it about 1/2" ever 1-2 weeks.

What size is your SWG? Pool Pilot Digital Nano
What % setting is your SWG? How long do you run it a day? 80% right now, runs 24x7. Have a variable speed pump that runs at 25% for 21 hours and 90% for 3.

What is your CYA testing history (ie May 1 CYA=X, June 15 CYA=X)? I don't have that recorded (I haven't been as diligent this year about recording it :-(

Full test results when I get home this evening. (I know the TA is high.) pH was at 7.2 as I just lowered it to start the SLAM.

 

[adeller]

Test results as of 6:00 this evening

FC - 12.5 (raised back to 18)
CC - 1.0
CYA - <20 (I added 26 oz yesterday, but don't expect that to show up yet)
pH - 7.2 yesterday at beginning of SLAM
TA - 80
CH - Unknown (tested to 70 drops woth no color change. I suspect the reagents could be old, they are original) last known value was about 320.

 

[duraleigh]

How old are your reagents? I am not yet suggesting that is a problem but a lot of your info is imprecise and leaves us dangling wanting more.

Actually, I have another thought....check your PM's.

 

[engrav]

Have subscribed to this thread as I too (in another thread) have CYA dwindles, not yet totally explained

my results are were
2/26/14 45
6/25/14 30
7/9/14 black dot visible with tube full
this AM after 2 lb yesterday 20-30

jblizzle commented that the test is plus minus 15 so you might have been 25 "a few weeks ago"
and with a little dwindle over "a few weeks" you are <20

chem geek also said
The loss at other times is not that unusual factoring in water dilution (backwashing/cleaning filter, splash-out, rain overflow) and slow oxidation of CYA by chlorine

it may be that "CYA dwindle" is a thing and that if one runs at CYA 30 or 40 which could be 15 or 25 one should check CYA q mo as does jblizzle

it also means that a serious CYA record is important at low ppm's because 45 then 30 with no significant events suggests next one will be <20

will be interesting to see your conclusions on "CYA dwindles"
thank you