Disappearing CYA

[wam525]

Welcome to TFP! I started a new Thread for your post. Please start a new Thread whenever you have a question or new topic as opposed to posting your question on someone else's Thread (we call that practice "hijacking"). Plus, posting your question in a new Thread is more likely to get responses and gives your question the attention it deserves. --BoDarville, TFP Moderator


I wonder how you can lose at much as 15 ppm CYA. Every year I lose nearly all the CYA over the winter, and I've never been able to figure out why. I just opened last week and the CYA was 10. But i just go to Sam's Club, buy a 50lb bucket of dichlor, and just use that to chlorinate until the CYA is up to 50. But i still wonder what happens to the CYA (and the alkalinity) over the winter.

 

[JasonLion]

Welcome to TFP!

Many people lose CYA over the winter. We believe that it is because of a strain of soil bacteria that knows how to break down CYA growing in the water.

 

[BoDarville]

Water replacement is by far the most common way for CYA to get lowered. While we often think of a drain & refill whenever the term "water replacement" is used, day-to-day splash-out can also lower CYA gradually but steadily. When I do lap swimming, I'm amazed at the amount of splash-out. Now imagine several kids in the pool splashing around.

There are, however, some other possibilities...

If you recently opened your pool, did you test the CYA after the pump was running for at least several hours (at least enough for one complete water turnover)? The CYA level can test differently when the pump has not been on in a long time, especially when opening a pool for the season. Other members have reported a similar phenomenon which may suggest that CYA stratifies in the water (e.g., settles towards the bottom of the pool) or that CYA has crystallized somewhere. Considering that you just opened the pool and that CYA is much easier to add than it is to lower, I would run the pump long enough for at least one water turnover (more would be better), retest, and post back with your results.

Another possible reason for CYA to drop dramatically is that some types of bacteria can actually consume CYA over the winter. Depending on the bacteria, the CYA can get broken down to ammonia or it can get broken down to nitrogen gas. This is not common, but it can and does happen.

If you are interested in a more technical read on this, check out this thread: Degradation of Cyanuric Acid (CYA)

 

[Richard320]

Welcome!

It sounds like you have a system that works!