Can CYA disappear with decent FC level?

[Ignoramus]

Hello, everyone!
I'm back with questions.

I am suddenly reading zero CYA in school pool.
Date: FC: CYA:
April 29. 7.5. 40
April 30 7.5. 30
+1.5 gal bleach
April 30 13.0
April 30. 13.5
May 1. 13.5
May 1. 11.5. 35
+0.5 gal bleach
May 3. 13.5. 40
May 6. 6.5 40
May 8. 7.5. 0

On May 7, I reloaded CYA reagent. First, I tested dad's pool and got no CYA reading, which was reasonable for the pool that became complete mess after flooding (his area got 10" of rain). So I didn't think anything was off.

But then I also get the same result at school pool, which looked nice and clean through all this time.

Do you all think that it is a bad reagent or that I suddenly got a problem in school pool that causes CYA to truly dissappear? If latter, what is it and how do I fix it?

Thank you!
Ig
Pool log: PoolMath Logs

P. S. I'm currently in third attempt at SLAMing the pool. Previous attempts were interrupted by torrential rains.
P. P. S. Dad's "complete pool mess" included solid green walls, liner that floated up and off the retainer ledge, water receding below skimmers, etc. We're still working on it.

 

[PoolStored]

it is a bad reagent

The CYA reagent is super stable and tends to last longer than most other reagents. If you changed one thing (reagent) and got a completely different result, it is likely the reagent (or testing procedure if that changed).

 

[Ignoramus]

The CYA reagent is super stable and tends to last longer than most other reagents. If you changed one thing (reagent) and got a completely different result, it is likely the reagent (or testing procedure if that changed).

We did have some 4" total of rain interspersed in those 10 days, but I tested after every rain and FC was never low.

 

[mas985]

P. S. I'm currently in third attempt at SLAMing the pool. Previous attempts were interrupted by torrential rains.

We did have some 4" total of rain interspersed in those 10 days, but I tested after every rain and FC was never low.

Overflow can cause you to lose CYA although what you are experiencing is pretty significant.

Do you have an autofill?

After the rain, are you allowing the pool pump to run a while for the water to mix up properly? You could be drawing from mostly rain although that does not explain the high FC but that could be due to the way you are adding FC which is?

 

[Ignoramus]

Overflow can cause you to lose CYA although what you are experiencing is pretty significant.

Do you have an autofill?

Not connected. But the pool level was very near full, just below the opening in overflow drain.

After the rain, are you allowing the pool pump to run a while for the water to mix up properly?

The pump runs 8 hours every night, so it should have been mixed well before I get my sample.

The sample is gathered at the depth of 1 ft in roughly the same spot every time.

You could be drawing from mostly rain although that does not explain the high FC but that could be due to the way you are adding FC which is?

I use liquid 10% chlorine from Pinch-A-Penny. Bottles are stored in unused, unlit building near the pool.

I pour bleach about 5 ft from the skimmer that collects more leaves (and so I think there is a better flow ro it).

Before this specific storm I fashioned floating chlorine tablet dispenser and added 3 tablets to it. I forgot to include it in my brief log, sorry.

Also, we have been in the pool for an hour, taking out drain covers and cleaning them, before sample with zero CYA was taken. No chlorine had been added for 16 hrs or so before that sample.

Thank you!

 

[PoolStored]

Reagent.

 

[Ignoramus]

Reagent.

Does it have expiration date?

it is 32 oz bottle, bought in January 2023. I've kept my spare reagents all in one bag in the fridge, and DPD powder (sealed) stored in the same bag caused labels to fade, and so I may be missing some info.

Thank you!

 

[PoolStored]

I reloaded CYA reagent.

I thought this meant it was new. It is still the only thing that changed.

Did you allow it to come to room temperature before you used it?

Again, CYA reagent is about the most stable (longest lasting) of all the reagents, but it is the only thing that changed...Occam's razor. And, you got same result in school pool...but unclear if they use CYA.

Did you test a second time?

 

[Ignoramus]

I thought this meant it was new. It is still the only thing that changed.

Previous tests were done with reagent from the same bottle, but that portion (obviouslyl was dispensed quite a while ago.

Did you allow it to come to room temperature before you used it?

Yes, it warmed up quite well.

Again, CYA reagent is about the most stable (longest lasting) of all the reagents, but it is the only thing that changed...Occam's razor. And, you got same result in school pool...but unclear if they use CYA.

School pool is my main pool and that's the one of concern here.

i do use CYA; originally added as powdered stabilizer, and then some from tablets in mandatory tablet feeder

Did you test a second time?

2 more tests. One sample was taken soon after zero reading, from a different part of the pool. Then one more this morning. All pretty much the same.

For what it's worth. I had once lost all cyanuric acid in the pool when I let it sit without chlorine for a week or so. At the time, we figured it were bacteria from the dirt blown into the pool that consumed CYA. After that I've been careful to keep FC up.

Thank you!

 

[PoolStored]

Can't be Ammonia, you are holding FC. It's a stumper.

I'd get some new reagent and see what happens...any other pool owners around you that might have reagent?

 

[AUSpool]

For what it's worth. I had once lost all cyanuric acid in the pool when I let it sit without chlorine for a week or so. At the time, we figured it were bacteria from the dirt blown into the pool that consumed CYA. After that I've been careful to keep FC up.

Thank you!

This is a bit off track from your current CyA issue so think about this independently from the current advice.

Bacterial distruction of CyA is a known and well documented process in sewage works. It requires zero FC, zero oxygen and a lengthy incubation time. A week wouldn’t be enough time. And if the pool was exposed to the air above the oxygen levels would have been too high. I’m very confident that this is not related to your current problem.

It sounds like your still using the same reagent that may be getting old. I would get new reagent and go from there

 

[Ignoramus]

Can't be Ammonia, you are holding FC. It's a stumper.

I'd get some new reagent and see what happens...any other pool owners around you that might have reagent?

I just ordered another bottle.

I'm getting dad into self-testing, and between the two of us, we'll consume it faster.

Thank you, @PoolStored !

 

[Ignoramus]

This is a bit off track from your current CyA issue so think about this independently from the current advice.

Bacterial distruction of CyA is a known and well documented process in sewage works. It requires zero FC, zero oxygen and a lengthy incubation time. A week wouldn’t be enough time. And if the pool was exposed to the air above the oxygen levels would have been too high. I’m very confident that this is not related to your current problem.

It sounds like your still using the same reagent that may be getting old. I would get new reagent and go from there

It may have been longer than a week. I'll check my notes.

Thank you!

 

[SJPoe]

Occam's Razor - the simplest solution is often the right one.

I had some 50ppm reference solution (R-7065) I was practicing with, and then accidentally used instead of the proper reagent (R-0013). The bottles were identical in my new test kit case, and I'd put the R-7065 in the slot the R-0013 usually occupies, and I didn't notice until the second time I tried the test and it came out at 0....

 

[Ignoramus]

Occam's Razor - the simplest solution is often the right one.

I'm such a newb, that I do not know which is the simplest solution.

I had some 50ppm reference solution (R-7065) I was practicing with, and then accidentally used instead of the proper reagent (R-0013). The bottles were identical in my new test kit case, and I'd put the R-7065 in the slot the R-0013 usually occupies, and I didn't notice until the second time I tried the test and it came out at 0....

Ignorance == confidence and so I didn't get reference solutions

Yesterday, I had realized that in my situation a reference would have been helpful.

My nickname is still accurate.

 

[Newdude]

My nickname is still accurate.

*can confirm. There's something(s) to learn everyday.

 

[Ignoramus]

Updated puzzle:

New reagent has arrived. Test shows CYA=40. Cross-check with old solution and it now shows CYA around 40 as well.

Hypothesis: The pool is very full, the skimmers are full to the tops, and surface action is weak. So I could have been testing in the weakly mixed layer of rain+pool water. It didn't occur to me to get a probe from the bottom.

Afterwards, we were in the water and then I began SLAM so the pump ran for 2 days, mixing the water well. And now I'm back to proper reading.

What do you all think?
Thank you!

 

[SJPoe]

I'm such a newb, that I do not know which is the simplest solution.

Ignorance == confidence and so I didn't get reference solutions

Yesterday, I had realized that in my situation a reference would have been helpful.

My nickname is still accurate.

In my line of work, I deal with complex systems and troubleshooting always starts with 'what changed ?'.
Everyone will tell me that they didn't change anything. They'll swear left is right, up is down, black is white that they didn't make any changes.
They'll come up with a myriad of esoteric solutions to ephemeral problems of dubious applicability, and then stake the company on that being the problem with no evidence or basis in fact.
Bonus points seem to be awarded for making sure the fantastical-frump-up is in someone else's sphere-of-idiocy...
Almost always, it turns out, someone changed something, and the law of unintended consequences resulted in it causing the problem.

In summary (and this is largely what Occam's Razor is really about) - don't go looking for complicated solutions when simpler ones can be tried first.

If your test was fine day after day after day and then suddenly isn't, what changed ? Something changed...or it would give you the right result.
That's not to say you KNOW what changed...but I guarantee something did. CYA is not going to disappear overnight unless some very specific conditions exist...most of which you'd be aware of if they did.
Seriously, if you find a way to remove 40ppm of CYA, overnight, let me know...we'll be rich.

New reagent has arrived. Test shows CYA=40. Cross-check with old solution and it now shows CYA around 40 as well.

Back in the day of the old switched telephone networks, we used to remove switch-relay cards, and put new ones in. The issue would be resolved. We'd then take the 'bad' card, and put it back where it was, and it would also work. This was so common, we had a diagnostic code for it - FWL (Fixed While Localizing) which was techy speak for 'dunno, works now tho'. Essentially the 'reseat' was enough to jiggle something or fix the bad connection...

Hypothesis: The pool is very full, the skimmers are full to the tops, and surface action is weak. So I could have been testing in the weakly mixed layer of rain+pool water. It didn't occur to me to get a probe from the bottom.

The biggest thing I try to teach the new guys at work is consistency and repeatability. If you do XX in testing, you should do YY in production. If you run your capacity test from 1-2am on Monday, you should run it at 1-2am on Tuesday. Reduce the variables as much as possible, and then when something DOES go wrong, you have less variables that you need to investigate.

I use a 3ft long piece of 3/4" PVC pipe, with cap on each end. Each cap has a 5/16" hole drilled in it. Put my thumb over the hole, put the pipe in the water to the mark half way up, remove your thumb. Count to 3, put your thumb back over, pull the pipe out of the water, point it at my little bowl, remove thumb. Basically a big 'straw' for the pool I now have about 4oz of water, from 2ft down. My pump runs 24/7, and I sample from the furthest point from the returns so as not to get 'fresh' chlorine from the SWG etc. Same spot every day.