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Thread: CYA loss after battle with Mustard Algae

  1. Back To Top    #1

    Join Date
    Aug 2013
    Rochester, NY

    CYA loss after battle with Mustard Algae

    Hi TFP!

    Just finishing a battle with mustard algae after neglecting my pool for over a week while in the hospital.

    I've had to keep my pool at shock / MA shock for days and clean ladders, equipment, and behind lights but I finally got it I think! I have pass the oclt two nights in a row and the brown dust is no longer reappearing.

    I have a few questions before I let me pool back down to normal FC levels:

    1) is it normal to lose CYA while consistently shocking your pool. My levels started around 50 but have dropped to below 30. I haven't back washed enough to justify this drop, IMO. Could it be a misreading with the test because of high FC levels? Or is the test accurate and should I maintain FC levels appropriate for 30 CYA?

    2) My pool water is a bit cloudy. My PH was a bit high before shocking, but I added acid. Wondering if the cloudiness might go away when I let FC down?

    3) there is still some slight yellow discoloration along the borders of the pool floor. I'm hoping these also go back to normal when my FC goes back down and I am able to check FC again. Can't imagine it is anything alive since I'm passing oclt x2.

    Latest test results:

    FC 20
    CC 0
    PH can't read atm
    TA 80
    Calcium 100 (Vinyl)
    CYA 30? See above

    Thank you all for the wealth of advice available on this site for helping me beat MA!!

    32 x 16 Vinyl
    Pentair Sand Dollar SD-60 Sand Filter
    Pentair Superflo (1.0 HP)

  2. Back To Top    #2
    Mod Squad JVTrain's Avatar
    Join Date
    Feb 2014
    Central Minnesota

    Re: CYA loss after battle with Mustard Algae

    It's likely a combination of some backwashing and CYA decomposition due to high chlorine levels for an extended period of time. There can be some decomposition of CYA at high FC levels.

    Cloudiness will not change when you drop the FC merely because the FC is lower. Cloudiness can only be decreased by increased filtration as long as nothing is growing in the pool. Look into the articles on adding DE to a sand filter to try to speed up the water clarity gains.

    Again, discoloration is not likely to change solely because the FC is lower. You may have some organic staining there (or metals staining) that may fade over time as you maintain proper FC levels. If it does not fade, it could be metals staining.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
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