CYA dropped & failed OCLT

[matt1097]

So i have been noticing over the last couple of weeks my SWG has been having trouble keeping up, so i have been slowly increasing pump time and percentage to try and find the balance. I am currently set at 13hrs a day at 45% on the SWG. I was initially chalking it up to the Florida weather getting hotter.
Then my chlorine started dropping faster. I finally tested CYA last night and i have gone from ~60 to effectively 0. (Today's Leslie's test says 24).

I have been raising the chlorine with liquid chlorine.
Last night at midnight i measured 11.5 FC. This morning at 9am, I measured 9.5 FC. At 2pm I measured 8.0PH, 7.5FC, and 0.5CC. Measured using a FAS-DPD test. All measurements here were with the TF-PRO kit.

In between the 9am and 2pm measurements, I took a sample to Leslie's to try and verify my own testing. Their numbers don't align to my testing at all, so I am mostly discounting them.
But that test result was ~12:30pm: 5.47FC, 6.26TC, 7.3PH, 57 alk, 24 cya, 0.3 cu, 529 phos, 3750 salt. It is the PH result and their lower FC that makes me question their calibration.

Is this ammonia? Everything i have read seems like my chlorine drop should be higher if it was.
Where else could my chlorine be going (especially overnight) that doesn't show as high CC?

It has been fairly dry the last few months, some rain this week. No water has been drained from the pool.

 

[Bperry]

So i have been noticing over the last couple of weeks my SWG has been having trouble keeping up, so i have been slowly increasing pump time and percentage to try and find the balance. I am currently set at 13hrs a day at 45% on the SWG. I was initially chalking it up to the Florida weather getting hotter.
Then my chlorine started dropping faster. I finally tested CYA last night and i have gone from ~60 to effectively 0. (Today's Leslie's test says 24).

I have been raising the chlorine with liquid chlorine.
Last night at midnight i measured 11.5 FC. This morning at 9am, I measured 9.5 FC. At 2pm I measured 8.0PH, 7.5FC, and 0.5CC. Measured using a FAS-DPD test

In between the 9am and 2pm measurements, I took a sample to Leslie's to try and verify my testing. Their numbers don't align to my testing at all, so I am mostly discounting them.
But that test result was ~12:30pm: 5.47FC, 6.26TC, 7.3PH, 57 alk, 24 cya, 0.3 cu, 529 phos, 3750 salt. It is the PH result and their lower FC that makes me question their calibration.

Is this ammonia? Everything i have read seems like my chlorine drop should be higher if it was.
Where else could my chlorine be going (especially overnight) that doesn't show as high CC?

It has been fairly dry the last few months, some rain this week. No water has been drained from the pool.

Looks like your FC got too low over the past few weeks and likely have algae starting to grow. Just need to start the SLAM process.

If you have ammonia, there would be zero chlorine holding in the water.

 

[matt1097]

That was the initial theory I was going with.
I had let it get <3ppm the last ~2weeks as i kept thinking i was close to getting the SWG tuned correctly. Lowest measured was 0.5FC, and this wild ride started shortly after that. So it all mostly checks

I am still confused at where the CYA is going. There isnt a ton of splashout, and the water I am removing for testing samples isnt anywhere large enough to account for even a 10% drop in PPM.

Does algae do anything to CYA?

Going back and looking at my Leslie's results over time (I really hate the subjectiveness of the home CYA test), I do now see a slow trend of dropping CYA i hadn't noticed before:

The only chemicals i have bought from them is muriatic acid.


So i am really trying to figure the CYA out to know if i should continue with it low until the OCLT passes or go ahead and bump up the CYA.

 

[proavia]

Pool store testing is not adequate - you need your own test kit to take charge of your pool water.
Test Kits Compared
While waiting for your test kit to arrive, add 5ppm liquid chlorine to your pool daily. Use PoolMath to determine the dosage requirement.

Pool store tests is inaccurate, inconsistent and not repeatable.
The only tests that are semi believable are the iron and copper results.

Have a read thru Pool Care Basics and a few of our YouTube videos https://www.youtube.com/channel/UCNgsSPdGSsja_Y2ZmVFaDKg

 

[matt1097]

I have my own test kit. I have the TF-Pro. All my numbers come from that kit. I edited the original post to try and make that clearer.
Per that kit, I filled the CYA tube and it was still completely clear.
So i have lost CYA.

Until my chlorine stabilizes I am trying to keep the chlorine >10 with 12.5% liquid chlorine.

I am looking for consensus on if i should ignore CYA right now, or do I need to figure out where it is going to not be chasing my tail.

 

[Bperry]

I have my own test kit. I have the TF-Pro. All my numbers come from that kit. I edited the original post to try and make that clearer.
Per that kit, I filled the CYA tube and it was still completely clear.
So i have lost CYA.

Until my chlorine stabilizes I am trying to keep the chlorine >10 with 12.5% liquid chlorine.

I am looking for consensus on if i should ignore CYA right now, or do I need to figure out where it is going to not be chasing my tail.

CYA degrades slowly and the CYA test has a +\- 10ppm tolerance at least. So if its reading low on your kit, get it up to 30 minimum and then SLAM. Then bring the CYA up to normal hot weather level.