Disappearing CYA

[UKjames]

When I opened my pool this year I noticed my CYA had dived from about 60 to negligible.

I didn’t check the cYA immediately before close so could have happened before but I’ve been diligent at keeping my FCl up above 7.5pct of CYA.

I never really closed the pool as no freezing to worry about and so ran the pump a couple of hours a day and kept my cl level around 11pct of CYA (well the cya I thought I had) but had to add liquid chlorine much less frequently.


could this happen or is leak or the most likely explanation? I needed to top up quite a bit over winter but the rate of top up has slowed down now so I think evaporation more likely the cause in increased water losses.

 

[cowboycasey]

You will lose about 3 to 5 CYA a month and colder weather seems to drop CYA faster.. To check in the winter when it is cold bring the water inside and let warm to 70 degrees then check CYA

 

[Texas Splash]

We do know that CYA will degrade over time somewhere in the rate of 3-5 ppm per month depending on the pool and environment. So if you last checked the CYA 8 months ago as as example it is conceivable that you lost 40 ppm of CYA in that many months. I would increase the CYA back to where you need it for now then monitor the level for a couple weeks to see if ti remains steady to rule-out a leak.

 

[UKjames]

Thanks CbC and Pat.

I thought the losses before were explained by backwashing- but didn’t check it that often as thought it was pretty stable. So I’m glad you’ve enlightened me.

When I realised CYA was gone I started making use of the pucks that have been languishing in the shed as I stopped using them when I discovered TFP and so it’s coming back up now.