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Thread: Stabilizing chemistry in pool with leak

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    Stabilizing chemistry in pool with leak

    Hi,

    Opener: I'm in the Dallas area and run my hose about 20-30 minutes each day during the summer to maintain a water level that keeps the skimmers from sucking air. I've got leaks around the tile and in the pool, have patched everything I find but still have to add water. Ultimately I will solve the leak issues with a pool remodel but until then I'm trying to keep chemistry stable. Recently the pool developed a dark color (black/brown/green) algae under the water line on most of the pool patch around tiles and cracks. Admittedly I've let the chlorine get low a few times this summer - noticeable by normal green algae on the sides of the pool which seems to be leaving a stain of sorts. I scrubbed around the tiles with a wire brush in case it is black algae (it was tough and I had to work at it), brushed down the sides of the pool and added liquid chlorine to SLAM.

    Pool info:
    About 35+ years old (I've had it two years)
    Approx 25,000 gal
    Originally gunite/plaster with fiberglass resurface and pool paint on the fiberglass

    Chemistry before SLAM:
    FC 2.4
    CC 0.0 to 0.5 (virtually undetectable)
    PH 7.6
    TA 110
    Borate 8-10
    CH 140
    CYA approx. 25ish

    My CH and CYA are chronically low - likely due to adding water frequently. I use Tri-chlor pucks in a floating feeder and liquid chlorine to supplement as needed.

    About 6pm I added 384 ozs of 10% chlorine - wanting to shock to FC 15ppm
    7pm it was 11.6ppm and I added another 128 ozs
    9:30pm it was 14ppm and I added another 128 ozs
    Next day 7am it was 16ppm - mission accomplished
    6pm (same day) it was 9.5ppm

    The water is crystal clear (it never was bad - just had the dark algae)
    CC is less than 0.5ppm

    The days are sunny and hot in Texas. Is it normal though to drop 6.5ppm of FC in one day? Do I need to shock back to 15-16 and if so, how long should I maintain that level? According to SLAM instructions I'm in pretty good shape with clear water and CC less than 0.5ppm. I'll check OCLT tonight. I'm hoping to have a pool full of people this coming weekend so don't want the chlorine too high.

    If I've done enough to combat the dark algae, what's the most important element of keeping everything else stable? Should I add stabilizer to bring up CYA so I'm not burning the chlorine so quickly? Is it important to bring up the CH? My PH and TA usually stay reasonable with minor tweaking of Borax and baking soda.

    Thanks in advance.

    Neil

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    Mod Squad pooldv's Avatar
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    Re: Stabilizing chemistry in pool with leak

    Welcome to TFP!

    With CYA that low yes, you will lose a lot of FC to the sun. CYA at 50 would be a lot better.
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    JoyfulNoise's Avatar
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    Re: Stabilizing chemistry in pool with leak

    So by my rough calculations, 30 mins of hose time at 6 gpm (standard garden hose flow rate) is roughly 180 gallons/day which when aggregated over a month yields about a 22% exchange of pool water with fresh water. In a 25,000 gallon pool, you'd need to add back about 2lbs of CYA every month to maintain a 50ppm CYA level. If you set you CH to 200ppm, the water loss would require you to add back about 8 lbs of calcium every month to maintain CH.

    You can probably maintain a consistent FC level with a leak like that but your leaks are definitely costing you a lot of money in make-up water and chemicals.

    Just throwing some rough numbers out there....I hope you can get the pool remodeled soon.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Stabilizing chemistry in pool with leak

    Thanks for the advice. I've ordered calcium and will pick up some stabilizer. I hope to be able to remodel after the summer season!

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    Re: Stabilizing chemistry in pool with leak

    Hello and welcome.

    Quote Originally Posted by nsamuelsen View Post
    ............
    9:30pm it was 14ppm and I added another 128 ozs
    Next day 7am it was 16ppm - mission accomplished
    At 9:30pm you added 128oz of 10% chlorine, but you do not post your OCLT starting FC level. Adding 128oz of 10% should have raised your pool to a FC of 18ppm. Did you check 30 minutes after your last chlorine addition as stated in the SLAM instructions to ensure your starting OCLT FC level?

    If the FC was indeed at 18ppm at the start of the OCLT, and 16ppm in the morning before the sun was on the pool then that is a failed OCLT (2ppm loss).

    Quote Originally Posted by nsamuelsen View Post
    ............
    According to SLAM instructions I'm in pretty good shape with clear water and CC less than 0.5ppm.
    According to SLAM instructions, your SLAM is completed when:
    1) The water is clear of any algae
    2) CC's are less than 0.5ppm
    3) You pass an OCLT

    http://www.troublefreepool.com/conte...tain-shockingl

    I believe that your SLAM is not finished.

    Dom
    Dom - TFP Guide
    Intex 18' X 48" Ultra Frame AGP 6700 gallons | Two Intex CS8110 SWG's | Hayward Pro Series 21" Sandfilter | Hayward 1.5HP Power Flo Matrix pump | Hayward Thru-wall Skimmer | Wanda the Whale | 72 sq ft of Sungrabber Solar Panels with Hayward GLC-2P-A | Taylor K2006 Test Kit, Sample Sizer & Speed Stir | Click Here To Become a TFP Supporter!

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    Re: Stabilizing chemistry in pool with leak

    Dom, you are likely correct. I did not check the FC 30 minutes after the 9:30pm add of 128 ozs. It definitely could have run up to 18 and back down to 16 by 7am as you mention - I didn't think of that and didn't focus on the OCLT test.

    Since then I've been focused on bringing up CYA to slow the rapid loss of chlorine to the sun. I added about 4lbs of stabilizer and tested 4 hrs later to find CYA at 32 and FC down to 8ppm. I just added another 3-4lbs of stabilizer to get it up around 50.

    I plan to add the calcium on Friday, then enjoy the pool over the weekend. On Sunday afternoon I could start the SLAM again. Do you think I should wait to see if I have continued algae issues?

    Thanks for all the advice!
    ~25,000 gals, free form 8.5' deep
    Pentair 18008 DE filter
    Pentair Challenger CHIIN1 main pump
    Polaris PB4 booster pump
    Taylor K-2006 test kit

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    Re: Stabilizing chemistry in pool with leak

    Quote Originally Posted by nsamuelsen View Post
    Dom, you are likely correct. I did not check the FC 30 minutes after the 9:30pm add of 128 ozs. It definitely could have run up to 18 and back down to 16 by 7am as you mention - I didn't think of that and didn't focus on the OCLT test.

    Since then I've been focused on bringing up CYA to slow the rapid loss of chlorine to the sun. I added about 4lbs of stabilizer and tested 4 hrs later to find CYA at 32 and FC down to 8ppm. I just added another 3-4lbs of stabilizer to get it up around 50.

    I plan to add the calcium on Friday, then enjoy the pool over the weekend. On Sunday afternoon I could start the SLAM again. Do you think I should wait to see if I have continued algae issues?

    Thanks for all the advice!
    Be careful with the CYA, it's been found that granular CYA takes a day or so (if using the sock method) after it's dissolved to fully develop in the test.

    8lbs (128oz) of granular CYA should add about 38ppm to your already 30ppm (25-ish would round up to 30). If you have it in a sock I would pull out whatever hasn't dissolved yet and wait 24 hours and test again.

    If the pool is clear, CC's are 0.5ppm or less, and your chlorine demand isn't increasing, there's no harm in enjoying the pool for a few days, then determine your next steps.

    BTW- it's safe to swim as long as your FC is above the minimum and at or below your SLAM level per your CYA.

    If this were my pool I would make sure my FC was at target and do a proper OCLT tonight. If that passes, the water is clear of any algae and not cloudy, and CC are less than 0.5ppm I would just maintain target FC and

    Dom
    Last edited by domct203; 08-09-2016 at 04:50 PM. Reason: Spelling
    Dom - TFP Guide
    Intex 18' X 48" Ultra Frame AGP 6700 gallons | Two Intex CS8110 SWG's | Hayward Pro Series 21" Sandfilter | Hayward 1.5HP Power Flo Matrix pump | Hayward Thru-wall Skimmer | Wanda the Whale | 72 sq ft of Sungrabber Solar Panels with Hayward GLC-2P-A | Taylor K2006 Test Kit, Sample Sizer & Speed Stir | Click Here To Become a TFP Supporter!

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