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Thread: Seems to be stable ... please correct my thinking

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    Join Date
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    Seems to be stable ... please correct my thinking

    First, thanks for such a great, informed (scientifically) forum. I'm getting my new home pool in order, and I think I have everything lined up, but want your thoughts on my thoughts --

    Pool size: 22k gallons
    Current chemistry:
    Salt (ppm) TDS FC (ppm) CC (ppm) pH Alkalinity (ppm) Corrected Alk Calcium (ppm) CYA (ppm) Sat Index
    2700 3410 2.5 0 7.8 110 57.5 190 150 -1.2

    I just acquired a Taylor K-2006 test kit and an ExTech portable salt tester. I probably need to add 30 lbs of salt. And the CYA is very high because the previous owner was using stabilized chlorine all the time (as he was getting lots of algae because his SWG sensor was broken and didn't know it - I've fixed that and it's generating Cl like a champ).

    I was considering adding acid to bring down pH, however given the corrected Alk value, I think it may be okay. Thoughts?

    Any other thoughts? Should I keep FC higher given the very high CYA?

    Thanks!

    ---------------------------
    Inground, 22k gallon, SWG pool with hot-tub and negative edge, DE filter, polaris, pebble plaster finish, lots of sunlight, warm climate
    Last edited by Ausmatt; 06-03-2015 at 08:42 AM. Reason: corrected Sat Index and added TDS

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    Scuba_Steve's Avatar
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    Re: Seems to be stable ... please correct my thinking

    First thing you need to do is get your CYA in line. Unfortunately that means draining quite a bit and refilling. This of course will throw everything else off.
    6425g Intex Ultraframe 18'x48" AG
    Stock 1500gph cartridge filter / Intex SWG CG-28669 with E.C.O.
    Install date: 5/26/2015
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    Richard320's Avatar
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    Re: Seems to be stable ... please correct my thinking

    Those look like pool store test results. Your high CYA could be even higher. I suggest you test it yourself. See Post 8 step 9.

    Let's say CYA really is 150. Is what you propose do-able? Short answer, yes. I've done it. I don't recommend it. There's a couple problems with running a pool with astronomical CYA.

    1) Even with a SWG, your target FC is 11. Figure CYA 70 plus CYA 80 means 5 FC plus 6 FC. There's no problem swimming in 11 FC if CYA is 150, but you can't trust the pH test results with FC above 10. Pictures that prove it. Do you really want to let FC dip so you can check and adjust pH and then hope the SWG can recover before algae takes hold? That kind of back and forth is anything but troublefree.

    2) If algae does get a start, it will take this much bleach to SLAM the pool.



    Shock level will be something around 59. The FAS-DPD kit can't read above 50. Oops. You'd need to drain then anyway.

    3) Every single FC test you do will have to be with the FAS-DPD test. Forget the easy quick check color matching. Better stock up on powder and drops.

    We make these recommendations based on experience - usually bad experience that desperate people share with us after the pool is a swamp and the pool store has maxed out the credit card and the kids are whining.
    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!

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    Re: Seems to be stable ... please correct my thinking

    Quote Originally Posted by Richard320 View Post
    Those look like pool store test results. Your high CYA could be even higher. I suggest you test it yourself. See Post 8 step 9.

    Let's say CYA really is 150. Is what you propose do-able? Short answer, yes. I've done it. I don't recommend it. There's a couple problems with running a pool with astronomical CYA.

    1) Even with a SWG, your target FC is 11. Figure CYA 70 plus CYA 80 means 5 FC plus 6 FC. There's no problem swimming in 11 FC if CYA is 150, but you can't trust the pH test results with FC above 10. Pictures that prove it. Do you really want to let FC dip so you can check and adjust pH and then hope the SWG can recover before algae takes hold? That kind of back and forth is anything but troublefree.

    2) If algae does get a start, it will take this much bleach to SLAM the pool.



    Shock level will be something around 59. The FAS-DPD kit can't read above 50. Oops. You'd need to drain then anyway.

    3) Every single FC test you do will have to be with the FAS-DPD test. Forget the easy quick check color matching. Better stock up on powder and drops.

    We make these recommendations based on experience - usually bad experience that desperate people share with us after the pool is a swamp and the pool store has maxed out the credit card and the kids are whining.
    Thanks. I am using a FAS-DPD kit (Taylor K-2006 and a calibrated electronic salt tester). I tested CYA twice, once the standard way and once with the 50% diluted method in the Taylor manual to make sure the results were this high (and because it only reads up to 100 CYA on kit). The results may appear like a pool store as I pasted them in from my Google spreadsheet I'm using to track my chemistry over time and see impact of various chemical additions. Are there any other tests for CYA than the stare at the black dot until it disappears method? Seems not terribly accurate.

    I appreciate your insights ... I guess there's no real way around the high CYA (thanks previous guy!) and the $60 to refill 10,000 gallons is probably a lot less than the chemical cost of dealing with major algae issues. Or as you highlight the need to drain 100% of the pool instead of 50%.
    ---------------------------
    Inground, 22k gallon, SWG pool with hot-tub and negative edge, DE filter, polaris, pebble plaster finish, lots of sunlight, warm climate

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    Re: Seems to be stable ... please correct my thinking

    After draining ~8000 gallons (with another 2000 gallons still in process of refilling - spillover basin), I'm please to report my CYA has plummeted:

    Date Salt (ppm) TDS (ppm) FC (ppm) CC (ppm) pH Alkalinity (ppm) Corrected Alk Calcium (ppm) CYA (ppm) Sat Index Notes
    6/3/2015 2700 3410 2.5 0 7.8 110 57.5 190 150 -1.2 Recommend draining 50% of pool and replacing
    6/3/2015 Replaced ~8000 gallons of water #N/A
    6/4/2015 2400 3030 1 0 7.8 110 78.5 200 90 -0.06 Add 23 oz muriatic; Add salt

    I think I'm pretty well set now going forward after adding a bit of acid today and then a sahara desert worth of salt. CYA should keep coming down from the ongoing basin refill, evaporative loss, and regular use from kids. I don't use any chemicals with stabilizer. In fact, I plan on not using any chemicals except for salt, acid, or baking soda.

    Thanks for the input from this forum and the valuable tools like PoolMath.
    ---------------------------
    Inground, 22k gallon, SWG pool with hot-tub and negative edge, DE filter, polaris, pebble plaster finish, lots of sunlight, warm climate

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    Texas Splash's Avatar
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    Re: Seems to be stable ... please correct my thinking

    Good to see that CYA comes down. You certainly have a way with numbers. Good to see you so comfortable with the process. Welcome to TFP!
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