Sudden drop in CYA

[Patgamen]

Just checked my CYA after Tropical Storm Gordon passed by us and I've had a significant drop in CYA ( 75 to 0). I did drain the pool twice during the three days of rain but I'm quite surprised for the CYA to drop so much over a period of a week. I last checked the CYA on Sep 1 and my CYA was around 70. My Cyanuric Reagent is fairly new so the test should be good. I checked CYA twice.

Some background. I switched from trichlor to Liquid Chlorine the beginning of June due to high CYA. I've partially drained the pool several times over the swimming season with little overall affect to the CYA. The CYA has been at a high of 90 and has averaged around 60 to 70 throughout the season until today. (I'm been using the Pool Math app since June)

The following are today's test results. I did just finish SLAMing the pool due to the start of an algae bloom. Does this make any sense? I know I have to trust the tests but I'm having a hard time believing that the CYA would go from 70 to zero in such a short period of time.

FC: 5.5
CC: .5
PH: 7.7
TA: 100
CYA: 0 - This is the first time I've ever been able to clearly see the dot on any CYA test I've done.

Thanks for any insight you can provide.

 

[YippeeSkippy]

You got a LOT of rain and it altered your pool water for sure! What else was altered?? Or did you add extra chlorine in advance of all that rain?

FL is the only area we hear from where the frequent rains allow for more leeway with the use of pucks or granular chlorine since the CYA gets washed out more often.

Maddie

 

[JamesW]

There is a bacteria that can eat the cyanuric acid and convert it into ammonia.

Since your fc got low, you might have had bacteria grow enough to eat the cyanuric acid.

Typically, you get a lot of CC and dropping pH during a SLAM where ammonia is present

 

[Patgamen]

I did add chlorine prior to the rains coming in to make sure I didn't get an algae bloom.

- - - Updated - - -

The PH rose for the first time this season from 7.4 to 7.7

 

[JamesW]

Also note that if you get a lot of rain, the rain can sit on top of the pool water for a while before mixing in, especially if the pump is off.

So, you might have gotten a lot of rain water in the test unless you made sure that the water was well mixed.

 

[domct203]

Also note that if you get a lot of rain, the rain can sit on top of the pool water for a while before mixing in, especially if the pump is off.

So, you might have gotten a lot of rain water in the test unless you made sure that the water was well mixed.

+1

You should always circulate the water for 20-30 minutes before taking a sample. Also, it’s best to take the sample from as far down as you can reach.

I put my collection bottle into the water upside down until I’m in the water up past my elbow, then I flip the bottle over to collet my sample.

 

[Patgamen]

Good idea. I'll try that in the morning. I did another test this morning after a full night of the pump being on and the CYA is still at 0. I've also turned on my chlorinator with triclor tabs in it for the first time this season and will continue to monitor the levels. The pool is clear and all the other tests look good.