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

Thread: CYA Discrepancy

  1. Back To Top    #1

    Join Date
    Jun 2010

    CYA Discrepancy

    Split by Moderator from HERE. Please start your own thread for your own questions. Thanks, jblizzle

    I'm going to hook into this thread since I was about to post a similar question.
    First my story.
    Just before the 4th of July I let the pool go for a couple of days. You know, busy.
    Look under solar cover to get a sample and it is a complete cloudy mess.
    FC at 0, CC at 3.5
    Just as a check, I take the sample to pool store and get the same story.
    They run some test called "Chlorine Demand" and it prints out I need to put in 48 pounds of "BurnOut 3"
    I start dumping in bleach. I test a couple hours later and FC is 0. Dump bleach, test and FC is 0.
    Do this for a a day and a half. Swore I dumped in 20 gallons of bleach in 36 hours and the FC was 0 each time.
    I read somewhere that the FC could be so high it would bleach out the test and never show red. I hoped this is what I did.
    But on a whim I did my CYA test. I had no reason to think it was low. Pool store had it at a good number (30 I think) and I was holding chlorine prior to this cloudiness.
    CYA was 0. Seriously, I couldn't believe it. My tube was crystal clear. Took a sample back to the store. CYA was 30.
    I dumped a pound of CYA in that I had on hand and a pound more a day later. 72 hours later my test shows 30 and the store shows 60.
    I'm still SLAMing right now and trusting my numbers for the work.

    How can the pool store numbers be so bad?
    26.7K gal. vinyl (16x38 - 8ft deep end), 1 HP Centurion pump, 300 lb Sta-Rite Sand Filter, Blue Sapphire cleaning robot, TF100 Test Kit

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: CYA Discrepancy

    There's no mystery. What you're describing is perfectly normal.
    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!

  3. Back To Top    #3
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: CYA Discrepancy

    Welcome to TFP!!!

    Typcially they do not do the CYA test with the correct lighting. So with not enough light, they are getting a higher result than you ... assuming you are doing it correctly outside with your back to the sun.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  4. Back To Top    #4
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: CYA Discrepancy

    This is quite rare, but it does happen. Once in a very long while, when FC levels fall to zero, a kind of bacteria that can break down CYA grows in the pool and some, or all, of your CYA disappears. The is often, but not always, accompanied by ammonia showing up in the water (ammonia is one of the possible breakdown products from CYA). Ammonia creates a huge chlorine demand, so that FC always reads zero until you finally add enough chlorine to burn off the last of the ammonia.

    As for pool stores, what is amazing is that some of them are correct once in a while
    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

Posting Permissions

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