Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 9 of 9

Thread: CYA levels and alkalinity

  1. Back To Top    #1

    Join Date
    Jun 2007
    Location
    Illinois
    Posts
    3

    CYA levels and alkalinity

    My CYA levels have been running high from the Dichlor and Trichlor I had been adding to my pool the last 4 seasons. I finally wised up and have switched to the BBB method. I had my CYA level checked 4 days ago and it had dropped from 150 to 115 after 2 drains and refills. My problem is that I have been using the Taylor test kit -2005 and my alkalinity levels are 150 but when I have my water checked at the pool store the alkalinity has been around 80. Does the pool store make any adjustments to the alkalinity that I should be doing? According to Taylor you should factor in your ph and CYA into a formula to get the correct alkalinity reading. When I did this I got a reading of 115. Any suggestions would be appreciated.

    Sunnyhoosier
    20x40 IG plaster w/spa, Polaris Autoclear SWG

  2. Back To Top    #2

    Join Date
    May 2007
    Location
    Houston, Texas, USA
    Posts
    148
    sunnyhoosier,
    Pool store testing is generally not reliable. The quick and dirty way to do this calculation is to subtract 1/4 of the CYA reading for a pH of 7.0-7.2 and 1/3 of the CYA for a pH of 7.4-8.0. Your outcome of TA 115 is pdc (pretty darn close).
    Poor Man's Pool
    Doughboy 18 ft round above ground
    7600 gal with center drain
    Pentair sand filter, 1 HP pump
    50 ppm borates
    "I know just enough to be dangerous"
    Pool Calc Ver 1.41 (Excel)

  3. Back To Top    #3

    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    28,408
    Poseidon,

    I am not aware of that formula. Is that applicable to all CYA testing? If so, we all need to get on board with it and start using it. Where did you find it?
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  4. Back To Top    #4
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,887
    Duraleigh - you might not have run into the correction factor because the default around here is to post "raw" numbers, ie without the correction. Unless your CYA is very high or your ALK is very low there is usually enough "play" in the values to not have to worry about calculating the adjustment. The time you need to worry about it is when all, or nearly all, of the ALK reading is coming from CYA. A typical case would be PH 7.5 ALK 90 CYA 45, corrected ALK 75. The difference between 75 and 90 will never really mater, so why worry about it. Now if you have PH 7.5 ALK 30 CYA 90 corrected ALK 0, then you would need to worry about it.
    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

  5. Back To Top    #5

    Join Date
    May 2007
    Location
    Houston, Texas, USA
    Posts
    148
    I believe waterbear posted that a while back at Poolforum (I could be wrong on that). Taylor seems to support it.
    Taylor Chemistry Topics
    Poor Man's Pool
    Doughboy 18 ft round above ground
    7600 gal with center drain
    Pentair sand filter, 1 HP pump
    50 ppm borates
    "I know just enough to be dangerous"
    Pool Calc Ver 1.41 (Excel)

  6. Back To Top    #6

    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    28,408
    Quote Originally Posted by Poseidon
    sunnyhoosier,
    Pool store testing is generally not reliable. The quick and dirty way to do this calculation is to subtract 1/4 of the CYA reading for a pH of 7.0-7.2 and 1/3 of the CYA for a pH of 7.4-8.0. Your outcome of TA 115 is pdc (pretty darn close).
    Well, I completely misinterpreted Poseidon's post. To me, it seemed he was saying that the CYA test needed the correction factor. i.e. if your CYA test is 60 with a pH of 7.5, then your CYA is REALLY only 40.

    That's my fault for not reading the post above yours carefully, Poseidon. I'm sorry I misunderstood you.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  7. Back To Top    #7

    Join Date
    May 2007
    Location
    Houston, Texas, USA
    Posts
    148
    duraleigh,
    No biggie.
    Poor Man's Pool
    Doughboy 18 ft round above ground
    7600 gal with center drain
    Pentair sand filter, 1 HP pump
    50 ppm borates
    "I know just enough to be dangerous"
    Pool Calc Ver 1.41 (Excel)

  8. Back To Top    #8
    Guest
    Quote Originally Posted by Poseidon
    I believe waterbear posted that a while back at Poolforum (I could be wrong on that). Taylor seems to support it.
    Taylor Chemistry Topics
    More than once I'm afraid. IMHO, the correction is more important when using stabilized chlorine that benefits from a higher TA to maintain pH stability and usualy means high stabilizer levels in the water if the stabilized chlorine has been in use for a while.

  9. Back To Top    #9

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,085
    My understanding is that the main purpose for adjusting the Total Alkalinity number to account for the alkalinity from CYA is to calculate Carbonate Alkalinity since that is what is important for calculating the saturation index. And has been pointed out, at normal pH of 7.5, 30 ppm CYA only contributes 10 ppm to TA so isn't a big deal while 90 ppm CYA contributes 30 ppm so is a little more important. So unless you are calculating the saturation index or are doing calculations for rates of carbon dioxide outgassing (as in this table where I assumed a CYA level of 30 ppm), then adjusting the TA level doesn't matter much. As waterbear points out, it is far more important to have a higher TA level when using an acidic source of chlorine (e.g. a TA of 120 when using Trichlor). Otherwise, a lower TA with somewhat higher pH or CH works fine.

    When we talk about lowering the TA level to reduce the tendency of the pH to rise, I have used a target of around 80 ppm as a lower limit for SWG pools where the CYA is kept closer to 80 ppm while I have used a target of around 60-70 ppm for non-SWG pools with lower CYA of 30 ppm. This is to have roughly the same carbonate alkalinity since that is what determines the rate of outgassing (along with pH and aeration).

    Borates also contribute to TA and technically would need to adjust TA for the same reasons as above, but even 50 ppm Borates only contribute about 5 ppm towards TA at a pH of 7.5 (they contribute about 16 ppm TA at a pH of 8.0).

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

Posting Permissions

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