CYA disappeared overnight two years in a row

[Pjbooth]

Good morning,

Has anyone ever experienced a dramatic decrease in CYA not attributable to adding fresh water, CYA removal kit use, or any other contributing factor? At this time last year, we experienced a dramatic drop in CYA over a few weeks. We were averaging upper 50's to 60 for the entire season until one point where it began to decrease and then dropped from 35 to 5 within a week. Of course, we were unable to maintain chlorine during this time and no one could explain how this could have happened. In fact, after daily trips to the pool store, I was eventually told I could not be telling the truth about the situation and they were done with helping me.

We opened the pool this year around 4/15/22 and had been running along quite well in spite of this until now. It is a 33,000 salt water pool with a heater and auto cover which we keep closed unless the pool is in use. Very little rainwater gets in the pool. Water analysis results below:

8/11/22
Salt 3950
pH 7.4
TA 78 (unusually low- usually 110's)
Ca 305
FC 5.9
TC 5.9
CYA 61

8/19/22
All results similar except FC and TC down to 0.1
Shocked and added stabilizer as our SWG recommends 60-80

8/26/22
pH 7.2
TA 148
Ca 283
FC and TC 0.2
CYA 19 (run twice)
8# of stabilizer, shock and pH plus added

8/27/22
pH 7
TA 139
Ca 304
FC 0.3
TC 2
CYA 46

Spoke to the Autopilot technician because we could not get a chlorine reading. He checked amps/volts and said we were making chlorine. He suggested manually testing the cell which we did. It bubbled immediately and we did a test strip which indicated chlorine being produced. He also suggested a super shock of getting the pool to 30ppm chlorine. I did that with 9 gals. liquid chlorine after getting the CYA up closer to the recommendation by the SWG mfr.

Test results the next morning indicated no chlorine in the water at all. I took a sample the next day and it was confirmed.
Salt 4050
pH 6.9
TA 130
Ca 308
FC 0.1
TC 0.3
CYA 89

We cannot get the chlorine level to normalize. I rechecked this morning after the SWG was on boost yesterday and still no chlorine showing. This is essentially the same scenario we had last year. I cannot believe it has happened again and there is no one who can give me an answer as to how it happened once let alone twice. I hope someone can help us.

 

[Texas Splash]

Welcome! Probably the most important aspect of your scenario is that your test results above are not from a TF-100 or Taylor K-2006C test kit. We at TFP can never over-emphasize the importance of proper testing from one of those kits. CYA does indeed degrade a little each month, and when it gets too low it's difficult to get a good reading, but without using of of those recommended test kits, a lot of what you are experiencing is guesswork and can be very frustrating.

I would recommend obtaining a TF-100 (link in my signature) or Taylor K-2006C test kit, then posting a full set of your own test results. We trust your own (proper) testing before a pool store or anything else. Until that time, you should have liquid chlorine on-hand to increase your FC right away before you get algae. Be sure to see our FC/CYA Levels for our recommended FC-to-CYA balancing.

I would also be mindful of you pH. Again, not sure we can trust those tests results, but your pH has been on the low end and that's not good for metal products (or plaster) in the pool. In fact, it would also help if you updated your signature with all of your pool & equipment info. It will help later. If you have any questions let us know.

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why shouldn't I use test strips? Our recommended test kits will pay for themselves in no time!

www.troublefreepool.com

 

[Bperry]

Good morning,

Has anyone ever experienced a dramatic decrease in CYA not attributable to adding fresh water, CYA removal kit use, or any other contributing factor? At this time last year, we experienced a dramatic drop in CYA over a few weeks. We were averaging upper 50's to 60 for the entire season until one point where it began to decrease and then dropped from 35 to 5 within a week. Of course, we were unable to maintain chlorine during this time and no one could explain how this could have happened. In fact, after daily trips to the pool store, I was eventually told I could not be telling the truth about the situation and they were done with helping me.

We opened the pool this year around 4/15/22 and had been running along quite well in spite of this until now. It is a 33,000 salt water pool with a heater and auto cover which we keep closed unless the pool is in use. Very little rainwater gets in the pool. Water analysis results below:

8/11/22
Salt 3950
pH 7.4
TA 78 (unusually low- usually 110's)
Ca 305
FC 5.9
TC 5.9
CYA 61

8/19/22
All results similar except FC and TC down to 0.1
Shocked and added stabilizer as our SWG recommends 60-80

8/26/22
pH 7.2
TA 148
Ca 283
FC and TC 0.2
CYA 19 (run twice)
8# of stabilizer, shock and pH plus added

8/27/22
pH 7
TA 139
Ca 304
FC 0.3
TC 2
CYA 46

Spoke to the Autopilot technician because we could not get a chlorine reading. He checked amps/volts and said we were making chlorine. He suggested manually testing the cell which we did. It bubbled immediately and we did a test strip which indicated chlorine being produced. He also suggested a super shock of getting the pool to 30ppm chlorine. I did that with 9 gals. liquid chlorine after getting the CYA up closer to the recommendation by the SWG mfr.

Test results the next morning indicated no chlorine in the water at all. I took a sample the next day and it was confirmed.
Salt 4050
pH 6.9
TA 130
Ca 308
FC 0.1
TC 0.3
CYA 89

We cannot get the chlorine level to normalize. I rechecked this morning after the SWG was on boost yesterday and still no chlorine showing. This is essentially the same scenario we had last year. I cannot believe it has happened again and there is no one who can give me an answer as to how it happened once let alone twice. I hope someone can help us.

If you have an auto fill, it’s possible for a water leak to cause constant CYA loss as it constantly replaces the water with fresh. But the pool store testing of CYA is usually the least trustworthy of their tests so don’t waste any effort trying to chase those results. Bad testing is a more likely cause of the problem.

 

[randytsuch]

If you buy a kit from tftestkits, I'd also get the cya standard solution

The CYA test can be subjective, this will help you to perform it.

 

[gingrbredman]

A lot of times, when someone is having a hard time with their pool, and are at their wits end with the pool store, chemicals, bouncing opinions and suggestions, they come here looking for help, but present the pool store test results to show something must be wrong, but the first issue is really the test results. Many a new member here has put a lot of faith in "free" testing and can not understand what is wrong, based on these numbers, that the other members here already know they can not be trusted. I only say this not to point out errors, but to point out why your own test kit is important to the problem solving process. If we looked at a set of pool store test results, and then came up with a plan of attack to fix the issue, the plan would be flawed because the test results are flawed. If someone has a set of results from their own test kit, the plan of attack is usually right on, and issues get resolved quickly.

Bad testing is a more likely cause of the problem.

Exactly! CYA doesn't usually disappear overnight, or even go from 60 to even 20 in two weeks. All bad data from the pool store most likely.

I cannot believe it has happened again and there is no one who can give me an answer as to how it happened once let alone twice. I hope someone can help us.

I can just about guarantee you, that with a proper test kit, and provided results in this very thread, you will find not just one, but a lot of people who will help you understand it, and help you. They will help with a plan of attack, an understanding, and all the tools you need for a future, trouble free pool. Many a member I was mentioning early did just this, and haven't had an algae breakout, cloudy water, or a tough time since.

 

[VinnyinNJ]

I have opened my pool once with it having no CYA and I was using a Taylor test kit at the time. How long it took to go to 0 I have no clue.

When I asked either here or at a different similar forum I was told it could have been a bacteria or type of algae that eats it (I forget which) and that was 10 or more years ago.

I agree that testing the water yourself will give you a better understanding of your water.

Edit: I should also add a more accurate reading.

 

[gingrbredman]

When I asked either here or at a different similar forum I was told it could have been a bacteria or type of algae that eats it

If CYA does in fact drop rapidly, it could imply bacteria which has converted the CYA to ammonia. This would also result in an inability for the pool to hold chlorine.

The title of the threat asks the question of how CYA can disappear overnight, but based on what I've read, there is nothing here that shows this actually happened, and without the test results, we can't be sure. The OP posted the question, and his PS results, even though we know the results are wrong, they also do not show a sudden drop to zero, Really, we are not sure what the CYA results were before, and what they are now.

Before the OP heads down the rabbit hole of chasing theories and guessing how to fix it.....

testing the water yourself will give you a better understanding of your water.

 

[deanr]

If it really did drop, then get an ammonia test kit from a pet store (ammonia is commonly tested in aquariums). If you have measurable ammonia, then you've identified what happened to the CYA and CL

Agree with everyone else; all the tests need to be your own tests with accurate test kit. Don't rely on anyone else to do it for you...