CYA loss over the winter

Lskul60

Well-known member
May 29, 2019
111
Long Island
Hi Everyone. Great to be back after a long, weird winter. Hope and trust everyone is safe, healthy and well.

Just opened the 16x36 inground vinyl (no heater) SWG pool over the weekend.

Water was mostly clear and I was off and running with my Slam. 48 hours later, the water is clearing up really nicely. These are my first results, which are great - other than FC and CYA

FC ~1.0
pH 7.4
Alk 70
CH 65
CYA <30
salt 3200

I realize I am getting very low FC, due to low CYA. But my issue is that I know that when I closed my pool in September that my CYA was 60-70. I know this because of all the data on my TFP pool math app.

I do realize that when I closed the pool, I drained approx 6 inches of water to get below skimmers, and have added that back now with approx 2,000 gallons of fresh water. Ok, I understand the dilution, but that's only approx 10% of my overall volume.

I have added 2 rounds of 2 pounds each CYA, as I understand the best practice is to add it slowly as to not overshoot.

I know I can and will get back to 50-70 CYA and be fine. But I am really curious of the CYA loss over the winter.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
29,261
Laughlin, NV
CYA loss over winter is a known phenomenon. Some times a bacteria will invade the water that consumes cyanuric acid. Its first stage is converting the CYA to ammonia. That creates a very high chlorine demand. Are you having that? If not, you were lucky and the process proceeded to conversion to nitrites. And you have no issues.
 

Newdude

Well-known member
Jun 16, 2019
3,065
NY
Great to be back after a long, weird winter.
Do you refer to the winter that was spring , or the spring that was winter ? What a ride this year for sure !!

do you have a permeable cover, or a solid tarp ? This off season was very wet and I haven’t seen the specs yet but it was at least on par with our usual 30+ inches of rain. I drained 12-18 inches from my pool twice this year due to rain. Even if you didn’t drain, it would have overflowed somewhere giving you a 1/2 + water exchange with no CYA.
 

Lskul60

Well-known member
May 29, 2019
111
Long Island
Do you refer to the winter that was spring , or the spring that was winter ? What a ride this year for sure !!

do you have a permeable cover, or a solid tarp ? This off season was very wet and I haven’t seen the specs yet but it was at least on par with our usual 30+ inches of rain. I drained 12-18 inches from my pool twice this year due to rain. Even if you didn’t drain, it would have overflowed somewhere giving you a 1/2 + water exchange with no CYA.

good old fashion solid vinyl cover. no overflow, no drain and exchange necessary
 
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Lskul60

Well-known member
May 29, 2019
111
Long Island
CYA loss over winter is a known phenomenon. Some times a bacteria will invade the water that consumes cyanuric acid. Its first stage is converting the CYA to ammonia. That creates a very high chlorine demand. Are you having that? If not, you were lucky and the process proceeded to conversion to nitrites. And you have no issues.
Thanks for your quick reply.

I'm hoping it's not ammonia, but with the water looking great and my CYA climbing back to nominal, I'm figuring another SLAM will cure everything. (usually does).

thanks again