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Thread: I thought my FC & CC readings would predict algae bloom?

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    Join Date
    May 2007
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    Milwaukee, WI
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    I thought my FC & CC readings would predict algae bloom?

    Hi All:

    For the past 5-7 days we have seen small amounts of green/yellow powder on the steps of our pool. The powder didn't feel slimy and easily dissolved into the water when we touched it. The rest of the pool looked fine. We watched our FC & CC closely, but they remained stable. Yesterday morning the pool was cloudy, but the FC levels hadn't dropped and our CC's were less than .5. By 6pm algae was growing up the sides of the pool, especially in the shaded areas. (We're assuming mustard algae.) Our FC value FINALLY showed a drop (2ppm since morning) and the CC's were still under .5. Since there was no doubt it was algae we shocked to yellow mustard level and began brushing. At 11 pm we tested the FC level again and it was still dropping. (Another 3ppm since 6pm.) CC was still reading less than .5. We added more chlorine and have been periodically testing and adding more chlorine when needed so the FC stays above shock level. We've dealt with algae before, we know what we need to do to kill it...so we're not worried about that aspect.

    However, I do feel stumped by the fact that our FC and CC levels didn't alert us sooner. Last year when we had this fine powdery stuff showing up on the steps we assumed it was pollen because our FC & CC stayed stable and we never got an algae bloom. (Here's the link to the post we made last year when we saw the powdery stuff:

    can-you-get-algae-if-fc-is-within-target-t2873.html

    Anyway, based on that experience, I thought that if an algae bloom was beginning, we would start to see a drop in the FC level (or increase in the CC's) BEFORE the pool turned green, algae grew up the sides, etc. If that's not always the case, is there any other way to detect a problem BEFORE you actually clearly see the green water/algae growth? (Besides testing FC every other hour, etc?) I know that the earlier you detect a problem, the earlier you can shock....the easier it is to clear the pool. From now on should I assume that slightly cloudy water means algae...not the pollen we've seen in the past? Or do I just have to accept that sometimes a bloom can occur within a matter of hours, and short of testing the FC's every other hour or so, there's not much else you can do to anticipate a problem in those cases? Thanks in advance for your help!!

    Readings at 1pm today: FC 20, CC .5 (Our CYA has been around 30-32 in the last week.)
    Still brushing & monitoring closely to keep our FC level high!
    22,000 Gallon, IG, Vinyl, Sta-Rite Sand Filter
    Milwaukee, WI area

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    JasonLion's Avatar
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    May 2007
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    Re: I thought my FC & CC readings would predict algae bloom?

    With green algae, you will almost always see a drop in FC before there is any visible algae. But with mustard algae, you see algae first and a FC drop second.

    There isn't much you can do about that other than maintain the correct FC level for your CYA level. If you start without algae, then as long as the FC level remains at the proper level you shouldn't get algae.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Join Date
    May 2007
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    Milwaukee, WI
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    Re: I thought my FC & CC readings would predict algae bloom?

    Thanks for your reply. The reason I'm confused is that our FC has never even dropped below 3 this summer, and with a CYA of approx. 30, our minimum FC should be 2.2. We've NEVER gotten close to that...or even seen a sudden/unusual change in FC. It's been stable all summer. That's what's confusing us...we test daily, our numbers are stable, and we keep our FC on the high end. (Looking back at our notes, it hasn't dropped below 5 in the last couple of weeks.) Our CYA dropped below 30 about a month ago, and we began using the auto chlorinator, could that be part of the problem?
    22,000 Gallon, IG, Vinyl, Sta-Rite Sand Filter
    Milwaukee, WI area

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    frustratedpoolmom's Avatar
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    May 2007
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    Re: I thought my FC & CC readings would predict algae bloom?

    My 2 cents...I don't think the autochlorinator use necessarily contributed. If you are certain the FC never dropped below the minimum...

    Honestly, Mustard Algae is just a tough bugger and is resistant to chlorine. That's why on Chem Geeks CYA Chlorine chart, he has you run with a higher minimum of FC to prevent it.

    viewtopic.php?t=2346
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Join Date
    May 2007
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    Milwaukee, WI
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    Re: I thought my FC & CC readings would predict algae bloom?

    Thanks so much for mentioning Chem Geek's Chart. We weren't using his Mustard Algae values as our minimum, but I think we'll start keeping our FC there from now on.

    Just when we think we know what we're doing...WHAM! Another lesson learned!
    22,000 Gallon, IG, Vinyl, Sta-Rite Sand Filter
    Milwaukee, WI area

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