Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 6 of 6

Thread: CSI/PoolMath wonky with extreme values?

  1. Back To Top    #1

    Join Date
    Jul 2014
    Location
    Prospect Heights, IL (NW Chicago)
    Posts
    64

    CSI/PoolMath wonky with extreme values?

    Not sure if this is a problem with the calculator or an odd inflection in the CSI formula or what...

    If you punch in certain values (which are close approximations of my pool currently unfortunately: PH = 7.2, TA = 110, CH = 675, CYA = 360, Salt = 0, Borate = 0, Temp = 83), then it shows a CSI value of -0.82...corrosion likely. That doesn't sound good. Well I figured the easiest adjustment is to increase PH since 7.2 is kind of low anyway and surely increasing PH would make corrosion less likely. However, if you keep those numbers but change the PH to 7.4, the CSI actually plummets down to -3.36.

    Here's a screenshot of the values using current and goal to see them side by side:


    I think the mega extreme CYA level and the very high CH level are just making the calculations wonky...if you increase PH further to 7.5, the CSI just goes NaN. Can anyone explain what's happening?
    40x20 IG gunite (~36K gallon). 6' attached spa with spillover. AquaLink RS OneTouch + SpaLink + iAquaLink 2.0
    450 sqft Sta-Rite cartridge filter, Sta-Rite single speed pumps (main, spa jets, booster)
    Coverstar Auto Cover, Polaris 280 cleaner, Taylor K-2006

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: CSI/PoolMath wonky with extreme values?

    That is happening because CYA can not be 360 when TA is 110, it is simply impossible. CYA contributes to TA, and a CYA of 360, with nothing else in the water, means a TA of at least 120. As a result carbonate alkalinity goes negative (internal to the calculations) and things fall apart.
    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

    Join Date
    Jul 2014
    Location
    Prospect Heights, IL (NW Chicago)
    Posts
    64

    Re: CSI/PoolMath wonky with extreme values?

    Quote Originally Posted by JasonLion View Post
    That is happening because CYA can not be 360 when TA is 110, it is simply impossible. CYA contributes to TA, and a CYA of 360, with nothing else in the water, means a TA of at least 120. As a result carbonate alkalinity goes negative (internal to the calculations) and things fall apart.
    Interesting. I need to redo my diluted CYA test at a couple of different dilution ratios to see if I can get some kind of convergence. My last test read somewhere between 70 and 80 with 1 part pool 4 part RO water sample, and that's where I was getting ~360.

    Is there a CYA:TA ratio? I never see in any threads it being mentioned that adding CYA will increase TA...and the "effects of adding chemicals" on the calculator doesn't state such a change.
    40x20 IG gunite (~36K gallon). 6' attached spa with spillover. AquaLink RS OneTouch + SpaLink + iAquaLink 2.0
    450 sqft Sta-Rite cartridge filter, Sta-Rite single speed pumps (main, spa jets, booster)
    Coverstar Auto Cover, Polaris 280 cleaner, Taylor K-2006

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: CSI/PoolMath wonky with extreme values?

    It's not a ratio, but rather that CYA contributes to TA, though the amount of contribution is a function of pH as follows:

    pH CYA factor
    7.0 0.231
    7.1 0.252
    7.2 0.271
    7.3 0.289
    7.4 0.305
    7.5 0.319
    7.6 0.331
    7.7 0.342
    7.8 0.351
    7.9 0.358
    8.0 0.364

    So at usual pool pH the CYA contributes roughly 1/3rd its amount to TA. So if you are measuring a TA that is less than roughly 1/3rd the CYA level, then something in your measurements is very wrong.
    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"

  5. Back To Top    #5
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: CSI/PoolMath wonky with extreme values?

    You are close to plausible values. Given the gigantic error range on a CYA test with dilution, your CYA could easily be anywhere from 280 to 440 (if your testing was perfect, a wider range is also plausible with anything less than perfect test technique). Your TA measurement is consistent with CYA from 330 on down, but the TA is +-10, so CYA could actually be 360 if TA was actually 120.

    Adding CYA doesn't really change the TA, but raising the PH back up to what it was before does. Once you have added enough base to raise the PH back up, the TA will have gone up by roughly 1/3 of the amount you raised the CYA level by. This isn't something you normally need to think about.
    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

  6. Back To Top    #6

    Join Date
    Jul 2014
    Location
    Prospect Heights, IL (NW Chicago)
    Posts
    64

    Re: CSI/PoolMath wonky with extreme values?

    Quote Originally Posted by chem geek View Post
    It's not a ratio, but rather that CYA contributes to TA, though the amount of contribution is a function of pH as follows:
    <snip />
    So at usual pool pH the CYA contributes roughly 1/3rd its amount to TA. So if you are measuring a TA that is less than roughly 1/3rd the CYA level, then something in your measurements is very wrong.
    Awesome...thanks for the info.

    Quote Originally Posted by JasonLion View Post
    You are close to plausible values. Given the gigantic error range on a CYA test with dilution, your CYA could easily be anywhere from 280 to 440 (if your testing was perfect, a wider range is also plausible with anything less than perfect test technique). Your TA measurement is consistent with CYA from 330 on down, but the TA is +-10, so CYA could actually be 360 if TA was actually 120.
    I was as careful and as accurate as I could be, but obviously I like the necessary tools to do it better than "kinda sorta not terrible". With lots of kids present over the holiday and some intentional draining and refilling, I wanted to test again anyway. So last night I made up two independent 1:3 dilutions and performed two tests each. I got 4 readings between 55 and 60, so I would say it is reasonable to believe I'm now in the 220 to 240 range. I had added some soda ash as well for PH so I retested TA as well and got 125. So at TA=125 and CYA=~230, things make sense and I'm actually around good CSI values. Now to replace 2/3 of the water to get CYA down around 80!

    Thanks for all the explanations and background information...it's much appreciated.
    40x20 IG gunite (~36K gallon). 6' attached spa with spillover. AquaLink RS OneTouch + SpaLink + iAquaLink 2.0
    450 sqft Sta-Rite cartridge filter, Sta-Rite single speed pumps (main, spa jets, booster)
    Coverstar Auto Cover, Polaris 280 cleaner, Taylor K-2006

Posting Permissions

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