Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 12 of 12

Thread: dots in bottom of pool?

  1. Back To Top    #1

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    dots in bottom of pool?

    Hello! So i noticed i have a few tiny brown/black dots on the bottom of my pool? They almost look like little rust stains? They don't brush off, i tried picking at it with my toe, couldn't feel anything and nothing came off. Is it algae? Water has remained clear, bbb method has been working great so far. Pictures attached, thanks!
    Attached Images Attached Images

  2. Back To Top    #2
    BoDarville's Avatar
    Join Date
    Jun 2012
    Location
    DFW, Texas
    Posts
    3,840

    Re: dots in bottom of pool?

    Before we immediately jump to the conclusion that this is black algae,


    Also, what type of surface does your pool have (e.g., plaster, fiberglass, vinyl)? Sometimes it is hard to tell from the pic.

    The fact that the water is clear is a good sign. Another possibility (a long-shot but I will put it on the table)...Did you recently get the pool refinished or recently move into that house and just now notice these spots? When I first moved into our current house (knowing nothing about pools at the time) I hired a pool tech to give me a "pool school" of sorts in showing me how to operate the equipment. When we got to the spa, we noticed similar spots. Pool tech first thought it was black algae. Turned out to be anti-slip particles about the size of the granules on an asphalt roof shingle.

    Let's post the test results and go from there.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  3. Back To Top    #3

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Thanks for the reply!

    The pool has a vinyl liner. We moved into this house about a year ago, and this is the first full pool season for us, and the first time we have noticed these spots. They are only in 1 small area of the pool...

    I may be very likely imagining this, but I think the spots have changed since I first noticed them. There may be a good chance I am imagining that, but I thought I would still mention it.

    Current test results are below, thanks!

    FC 8.5
    CC .5
    pH 7.7
    TA 110
    CH 190
    CYA 60

  4. Back To Top    #4
    BoDarville's Avatar
    Join Date
    Jun 2012
    Location
    DFW, Texas
    Posts
    3,840

    Re: dots in bottom of pool?

    Your test results look good. Just keep an eye on the CC. At 0.5 ppm you are just below the threshold of needing to SLAM. You can also try an Overnight FC Loss Test. That test may provide more insight as well. If you lose more than 1 ppm of FC on the Overnight FC Loss Test, please post that fact.

    One other quick test you can perform to see if the stains might be metal-based is to try rubbing a vitamin C tablet on a couple of the stains for about a minute or so. If the stain lifts, then it is a metal stain. If that's the case, please post your findings.

    In the meantime, I would continue keeping FC in the range of 8-10 ppm which is at the high end of the recommended range for your pool's CYA (see Chlorine CYA Chart), and brush the spots with a nylon or similar soft-bristle brush (no stainless steel on your vinyl liner) at least once a day. See if the spots diminish or go away after a week or so.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  5. Back To Top    #5

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Thank you very much, I'll test tomorrow morning and post results.

  6. Back To Top    #6
    Melt In The Sun's Avatar
    Join Date
    Oct 2009
    Location
    Tucson, AZ
    Posts
    3,899

    Re: dots in bottom of pool?

    If you can't scrape anything off, it's not black algae...though the shape of the spots certainly resembles it. If you put on some goggles and dive down there, black algae will look like little fuzzy slimy bumps, and will easily scrape off on your fingernail.
    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!
    TF Test Kits -- PoolMath -- Pool School
    Make each day your masterpiece. - John Wooden

  7. Back To Top    #7

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Yeah, i brushed it pretty hard and nothing came off at all. Overnight chlorine test showed a 1ppm drop in fc. Think i may SLAM just to be safe? Though it's supposed to be hot this weekend so i may wait.

  8. Back To Top    #8

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Update!

    So I finally got some goggles and took a dive down there... it is not algae.

    It looks like little brown rust spots. I can pick at them with my fingernail and get a little smear, but not much comes off. So what is causing these rust stains? What's the best way to get rid of them? Vitamin C tablet?

  9. Back To Top    #9
    linen's Avatar
    Join Date
    Jul 2010
    Location
    Twin Cities, MN
    Posts
    8,649

    Re: dots in bottom of pool?

    Yes, if the spots are rust, vitamin C should get rid of them.

    As to where they came from, it looks to me as if small metals "grindings" got in your pool?
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  10. Back To Top    #10

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Well, I am surrounded by farmland... maybe some fertilizer blew into it, and some iron got in? That's the only thing I can think of...

  11. Back To Top    #11

    TFP Guide

    chiefwej's Avatar
    Join Date
    Jun 2011
    Location
    Tucson
    Posts
    2,853

    Re: dots in bottom of pool?

    If its an inground pool, has anyone fertilized grass near the pool?
    chiefwej
    Tucson, AZ
    16x36 rectangular (19k) Pebble Tec play pool/spa, Pentair Intelliflo VS 011018, Super II 2hp (spa), Aqua Rite T-15 SWG, Pro Grid 60 DE, Hayward H400 & Heliocol Solar heating, A&A infloor system, fill water w/high CH and TA, 50 ppm borates,TF-100 test kit

  12. Back To Top    #12

    Join Date
    Nov 2012
    Location
    Illinois
    Posts
    20

    Re: dots in bottom of pool?

    Quote Originally Posted by chiefwej
    If its an inground pool, has anyone fertilized grass near the pool?
    It's an above ground pool, with no fertilizer on grass near it.

    I can only think of 2 ways metal could've gotten in there...

    Either fertilizer or something blew into it from the fields near my house.

    Or, it is in the water I put in. I haul water from a nearby town, not sure if that could have metal or not...

    Would it hurt anything if I leave the spots alone? I can try to rub vit C tabs on them, but there are a good number of little spots. I read about the ascorbic acid treatment, maybe I could do that in a month, when it gets cold and I'm about to close anyway. Any other options?

    Thanks!

Posting Permissions

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