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Thread: Why metal stains?

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    Why metal stains?

    Had a couple of dime sized stains when I took over the pool. They disappeared when I got the pool balanced, keeping the pH around 7.5/7.6 July through October. I let the pH rise to 7.8/7.9 through the colder months with no stains.

    In the last couple of weeks I've dropped the pH back down to 7.5/7.6 as the temp has risen. In the last week about 30 small stains have appeared, mainly on the shallow end steps.

    That doesn't make sense! The only factor I can think of is that as about 6 weeks ago I raised CYA to 50 with 4 pucks dissolving over 3 weeks in a Rainbow feeder half open. FC remained consistent at 7, but pH dropped to 7.2 so I added pH up. Added way too much and had to add MA to bring it back down, all within a couple of hours. Stains have only appeared in the last week, and do appear to fade after MA addition.

    Why am I getting these stains at the lower pH? Am I heading for an AA treatment or should I drop pH to 7.2 for a few days and see what happens?

    Last nights test results:

    Temp 78
    FC 7.5 (after small Cl addition)
    PH 7.5
    TA 80
    CH 350
    CYA 50

    Mike
    Built 1980, 19' x 30' almost rectangular, screened 15,000 gal, plaster, Hayward DE 3620 filter (currently using cellulose), Emerson 1081 1HP pump, AquaCal Heatwave SuperQuiet SQ110R heater, Zodiac T5 Cleaner, Taylor K-2006 test kit

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    Mod Squad tim5055's Avatar
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    Re: Why metal stains?

    Are you sure try are metal stains?
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Why metal stains?

    Yes, checked with vitamin C tab.
    Built 1980, 19' x 30' almost rectangular, screened 15,000 gal, plaster, Hayward DE 3620 filter (currently using cellulose), Emerson 1081 1HP pump, AquaCal Heatwave SuperQuiet SQ110R heater, Zodiac T5 Cleaner, Taylor K-2006 test kit

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    JasonLion's Avatar
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    Re: Why metal stains?

    They are probably iron stains.

    Iron staining happens when PH is higher, when water temperatures are higher, and when FC levels are higher, or some combination of those three.

    AA will help remove existing stains, but to prevent the stains from reappearing you either need to remove the iron from the water (not always possible) or use sequestrant. Sequestrant will bind to the iron and prevent it from forming stains. However sequestrant breaks down slowly, so more needs to be added regularly.
    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

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    Re: Why metal stains?

    pH has been lowered from cold water values, FC always kept within correct CYA range. Seems to be iron spots in the surface of the plaster around the steps.
    Built 1980, 19' x 30' almost rectangular, screened 15,000 gal, plaster, Hayward DE 3620 filter (currently using cellulose), Emerson 1081 1HP pump, AquaCal Heatwave SuperQuiet SQ110R heater, Zodiac T5 Cleaner, Taylor K-2006 test kit

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    JasonLion's Avatar
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    Re: Why metal stains?

    Staying in the recommended ranges is not sufficient to prevent iron staining when there is iron in the water.

    I forgot to mention, the iron level in the water also effects the chances of iron staining.

    One more possibility, if the stains always show up in the same few spots they might be caused by iron inside the plaster that is too close to the surface. This would not apply if the stains are extensive or appear in different places each time.
    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

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    Re: Why metal stains?

    The pH for water above the steps if they are shallow will be higher than the bulk pool water unless you've got continuous water flow over those steps. The reason is that carbon dioxide outgassing will raise the pH and in a shallow area with little water mixing the pH will stay high. Higher pH precipitates more metal stains.
    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"

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    Re: Why metal stains?

    Sounds plausible. I just measured pH 1ft out and 2 down from the deep end (6ft) and right in the corner of the shallow end steps. 7.4 at both (I dropped it a little after last nights test). Pump hasn't been on for 3 hrs. I'll add my once every 2 days MA (about 5 oz) in front of the return jet opposite the steps at the shallow end to see if that helps.
    Built 1980, 19' x 30' almost rectangular, screened 15,000 gal, plaster, Hayward DE 3620 filter (currently using cellulose), Emerson 1081 1HP pump, AquaCal Heatwave SuperQuiet SQ110R heater, Zodiac T5 Cleaner, Taylor K-2006 test kit

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