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Thread: Pretty sure I have mustard algae - HELP

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    Join Date
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    Pretty sure I have mustard algae - HELP

    Been slamming for 3 days
    CYA 45-50
    TA 130 (I use trichlor)
    pH - 7.3
    FC - 22
    CC - varies during the SLAM, 0 - 2.5

    I've been maintaining FC 20. My CC has been as high as 3.0. During the day the water is crystal clear but there is mustard colored stuff on my vinyl liner, think dark brown mustard color. As hard as I brush it has no effect. I really thought I had the algae beat until the last hour. FC wasn't dropping and CC = 0.

    Within 60 minutes of the sun going down and me scrubbing pool earlier there is now a dark mustard stain to everything. Brushing has no effect.

    This is with CYA 50 or less and FC 22, CC =0. I'll keep slamming but wanted any help. I've followed TFP guides for years with great success and am at a loss on this one.

    It's the fact that the plastic chairs were clear during the day and within 60 minutes turned mustard brown once the sun went down, even with a FC of 20+ that has me concerned.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    Texas Splash's Avatar
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    Re: Pretty sure I have mustard algae - HELP

    Spidey07, this one has me puzzled for a couple reasons, and I'll throw a few thoughts back at you for consideration. Let's see if we can put out minds together and crack the code here.
    - Mustard algae is a yellow/green color and usually grows on the walls and floor mostly on the shady side of the pool. If you do shock the pool, mustard algae will mostly disappear as long as you are at shock level and brushing occasionally. There are a few more specifics about MA on the Pool School - Mustard Algae page. I'm not so sure what you are seeing is MA because as annoying as MA can be for some pools, it generally will disappear at shock level and certainly show improvement with brushing - something you have been doing a lot of recently with no change.
    - Your pH is current on the low end. Good when starting a SLAM, but I would've expected it to be higher given the fact your FC is so high and generally pH increases during a SLAM. I'm wondering if your pH is actually too low and a bit corrosive.
    - Speaking of acid, you noted above "TA 130 (I use Trichlor)". Not sure why? Do you mean you are using tabs to try and lower TA? That might explain the low pH as well.
    - I'm not understanding the description of "plastic chairs" (sorry). Pool furniture perhaps? But why everything would take an apparent shift in color within an hour is very odd.
    - Other than regular liquid bleach, have you added anything else to your water?
    - Your CCs are still fluctuating correct? So that does seem to indicate "something" is overwhelming your water. You have no other equipment other than your filter and in-line chlorinator?
    - Any metal objects that could be showing signs of rust or change in your pool?
    - When was the past time you deep cleaned your sand? If it's been a while, you might want to refer to the Deep Cleaning a Sand Filter page.

    My initial comments alone may not solve this mystery, but with some more information and brainstorming, we should be able to find out why your CC is bouncing up & down and what is causing the discolorations.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
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    smforte's Avatar
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    Re: Pretty sure I have mustard algae - HELP

    Sounds like possible metals with the plastic turning. Try crushing up some vitamin C pills, put in a sock and hold it to the plastic. If it clears it's metal staining. Possible iron.
    Montgomery, AL
    27000 16 x 36 IG, Vinyl, Grecian, Hayward Sand filter, 1 HP Pentair whisperflo motor, Aqua Genie filter not by choice, no extra jets, Dolphin s300i robotic cleaner,Taylor K 2006 test kit, speed-stir which I couldn't live without!

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    Re: Pretty sure I have mustard algae - HELP

    Thanks Texas. The chairs I'm talking about are plastic chairs that are built into the pool and covered by water. What has me puzzled is the water is clear and an hour or two after it gets dark these plastic chairs are covered in a deli mustard stain that I can't brush off. It all started when I let my FC get too low, water temps shot up and I had lots of folks in the pool. My fault for that...thinking back I know exactly what happened to my FC (water temp shot up 6 degrees, I wasn't testing daily, increased people factor).

    Overnight chlorine loss test is good. So I'm passing 2 of the 3 for a good SLAM. Water tests are good but I'm still dealing with the discoloration of the liner and pool chairs. Water is crystal clear but liner has algae discoloration that I can't brush off.

    FC 23
    CC 0
    pH - can't test, FC too high
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    Texas Splash's Avatar
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    Re: Pretty sure I have mustard algae - HELP

    Is there a back & forth patter with the discoloration? By that I mean does it lighten at all in the day then get dark again at night, or did it all just seem to stain that one evening and now it's the way all the time? As long as you've had the pool, did you ever have a staining issue before? Any chance you do have metals in the water? We know metal will precipitate-out onto things in the pool when the FC is elevated high. I'm wondering if on that one day, when you noticed FC was low, that when you increased FC it caused a reaction to metal? Might not be a bad idea to try the vitamin C test as smforte suggested.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

  6. Back To Top    #6

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    Re: Pretty sure I have mustard algae - HELP

    Thanks Texas, I really appreciate the help as I thought I knew what I'm doing pretty well but this has me stumped.

    History of the pool is I've never had any metal staining problems or anything else that couldn't be solved with a shock/slam. In fact I've rarely had to SLAM the pool during the season as I test every day, only on opening and closing.

    Your point about a pattern - yes there is a very clear distinct pattern of the discoloration and it only started when I raised FC to shock level. During the day these plastic chairs are pretty clear but once the sun sets they look like somebody sprayed them with dark mustard paint. They are do have a texture on them so the iron precipitating is a nice lead and good direction. It's that it only happens at night is what is so weird and why I was leaning algae.

    I did have something growing in my water as evidenced by the high CC and rapid FC loss during SLAMming. I'll try vitamin test but never had any metal staining trouble before. I'll keep testing/slamming but pretty sure I've killed what was growing in the water.

    Water is crystal clear and sparkly

    -edit-
    FC 23
    CC 0

    CC been zero for 24 hours now, passed overnight chlorine loss test so nothing is growing in the water I believe.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    Texas Splash's Avatar
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    Re: Pretty sure I have mustard algae - HELP

    We've had some other members discover that even though they never had metal before, something changed locally in their water source within the city and all of a sudden metals were present. So if you rule-out any metal presence through various testing, then I would continue the SLAM at a normal level. Once you pass the 3 SLAM criteria, you do have the option of raising the FC to mustard algae level, but only do that for 24 hours. My gut tells me it's not MA though. But if you rule-out metal or anything else, I suppose it can't hurt just for a one-time 24 hr MA shock level to see if it effects anything for the better. Oh, and don't forget the filter deep cleaning if you've never done it before or it's been a few years. Can't hurt. Keep us posted, and have a nice day.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

  8. Back To Top    #8

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    Re: Pretty sure I have mustard algae - HELP

    Thanks again Texas, I'm leaning metal now based on water tests just performed and what I tested today before sun up and looking at my log. I'm not losing any CL and no combined chlorine, been that way for 24 hours. You guys really pointed me in the right direction, thank you.

    It's that the staining gets so bad after the sun sets that puzzled me. It's extremely dramatic, those plastic chairs are white and then when sun sets it looks like you spray painted them with brown mustard.

    I'll report back with vitamin test. We're lucky here in Louisville to have very, very good water.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

  9. Back To Top    #9

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    Re: Pretty sure I have mustard algae - HELP

    For reference and others.....

    FC - 16 (sunny day no additional Cl added)
    CC - 0

    No more staining, sun has set for a while now. Water and pool are sparkly. SLAM successful but I think I ran into an iron/metal thing when I elevated FC
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    Mod Squad pooldv's Avatar
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    Re: Pretty sure I have mustard algae - HELP

    Crush up some Vit C tablets in a sock or knee high and rub it on the stains for a few minutes. If it lifts the stain then it is metal.
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