Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 4 of 4

Thread: Disappearing CYA

  1. Back To Top    #1

    Join Date
    May 2014
    Towson, MD

    Disappearing CYA

    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.

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Disappearing CYA

    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.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3
    BoDarville's Avatar
    Join Date
    Jun 2012
    DFW, Texas

    Re: Disappearing CYA

    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)
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  4. Back To Top    #4
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Disappearing CYA


    It sounds like you have a system that works!
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts