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Thread: Why does rainwater make bathtub rings?

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    Why does rainwater make bathtub rings?

    Every time it rains my fiberglass pool gets bathtub rings almost instantly. When my water is balanced and absent of rainfall, everything is fine. Anyone have an idea what is in the rain to create these rings? They appear black in color.
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump

    NC KANSAS44

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    Melt In The Sun's Avatar
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    Re: Why does rainwater make bathtub rings?

    As rain falls, it washes dust, pollen, etc. out of the air. Maybe that's it? Does any rainwater flow into your pool, off the decking or something?
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Re: Why does rainwater make bathtub rings?

    Quote Originally Posted by Melt In The Sun
    As rain falls, it washes dust, pollen, etc. out of the air. Maybe that's it? Does any rainwater flow into your pool, off the decking or something?
    Not that i have ever observed. The deck is very sloped outward, not that it would be impossible i suppose.
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump

    NC KANSAS44

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    Re: Why does rainwater make bathtub rings?

    I agree with MITS. It's probably just the dust that comes with the rain.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Re: Why does rainwater make bathtub rings?

    I think the pH of rain has a lot to do with what's in the air and mixes with rain. Many places have acid rain. Here we have usually "neutral" pH (relative to the pH of pool). Sometimes it may be a little alkaline, though, mixing with the chalk and clay dust.

    Thinkly, are you near, or surrounded by major metropolitan area(s). How about the prevailing winds. Where do they usually come from. Any factories within a few hundred miles? We get a lot of dust that blows in from far west Texas, hundreds of miles away. As I'm south of Dallas/Fort Worth, with winds and storms mostly from south, and southwest, in summer, we don't get the pollution from the Metroplex mixed in our rain; just lots of dust from sparsely populated areas.

    People who live in urban areas usually have dust mixed with pollution and it is darker in color than what we have from our mineral dust/powder.

    Last year, one of our member's neighbor's house burned down. Her pool was a greasy oily mess due to the fire close by.

    gg=alice
    1981, 25K, IG, Blue Plaster 1996, somewhat oval, widens a bit at shallow end, 1.5" pipes, 2" at Pad, 1 separate main drain, 1 skimmer, 4 returns + dedicated cleaner return, 10 ft deep end with very fast decline from shallow, Pentair Quad 80 DE, Pentair Intelliflo VF, 3/4 HP Booster Pump (equipment pad about 8 ft below top of pool), Challanger 3/4 Trash/Emergency Pump 120v, Polaris 280 (pressure), iRobot Verro cleaner (robotic), Aquabot Turbo (robotic), Jacuzzi Tracker 4X (vacuum) Pool Blaster (Buster), Two (2) PoolSkims, Solar Breeze (solar powered top skimmer) (beta to ver. 2, release date 2010), ColorSplash LED replacement bulb. Aries 550 gal separate spa, 2002 (our 3rd and BEST spa) , BBB-Bromine

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    Re: Why does rainwater make bathtub rings?

    How do you get the dark bathtub ring off? I have the same problem with my fiberglass pool. Every single time it rains it's a lot of work to get it clean. I have tried everything. Something someone told me to try is a fine piece of sandpaper. Lightly scratch and wipe clean with a damp rag. I'm always a little nervous I may be getting some metals in the pool from the sandpaper. But, I try to be very careful. This is the only thing that really works. Do you have any ideas?

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    Butterfly's Avatar
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    Re: Why does rainwater make bathtub rings?

    Welcome to the forum

    Suntan lotions, oils and other sticky stuff can get stuck at the water level and can turn black from dirt and debris.

    You can try a scum bug to help prevent this and try a magic eraser instead of the sandpaper on the scum line!

    Also, make sure your pool is balanced. Post a full set of test results & we'll check them out with you.

    Folks need to make sure that their oils/lotions are applied and allowed time to soak in/dry before they take the plunge!
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    Re: Why does rainwater make bathtub rings?

    It's the stuff you can't see sticking to the side of the pool. As the water level changes, it gets deposited at another level.

    A little baking soda sprinkled on a wet sponge, & a little elbow grease , will usually remove it.
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