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Thread: CYA increase from ~25-30ppm to ~45-50ppm 2 questions

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    CYA increase from ~25-30ppm to ~45-50ppm 2 questions

    I recently increased my cya level and I am wondering if it is normal with this increase to go from having to add bleach daily to now every couply of days? My Chlorine levels are barely moving and I am in direct sun all day long. In fact, here in NC we have had over 100 degree ambients for the last week.

    (18000 gal 16x32 inground)
    My numbers are:
    ALK - 90
    CYA- 45-50
    FC- 6
    CC- 0
    PH- 7.2
    TEMP- 91

    I'm not complaining, just wondering how long it will take for the FC to start to drop off.

    ALSO- on the chlorine / cya chart it shows a column for mustard algae FC target and shock: Question- is the mustard algae FC target & shock only if you have mustard algae, or if you are treating it, or if you are prone to get it? This is the type of algae that we typically see in our pool and I want to be sure I am reading the chart correctly.
    Thanks in advance.
    -Dan

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    frustratedpoolmom's Avatar
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    The CYA will help protect the Chlorine from UV rays, which sort of destroy it. If you had no CYA, the Sun would eat up all the chlorine in a day. So with CYA, your chlorine is much more "stable" which is why it's also called stabilizer.

    It'll drop in a day or two, especially with kids swimming.... NO worries.

    Yes, that level is if you get those algea, not to prevent. the "target" fc level is what you are shooting for, and don't go below "minimum".

    If you stay in those ranges it would be VERY unlikely you'll develop any algea.

    Enjoy!!!
    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
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    Prov,

    I'm sure most of us are jealous of your low chlorine consumption...I know I am.

    Would you mind tracking that consumption? Simply test the same time each day for a few days in a row and post your results (of course, post any additions to Cl that you make)

    Mustard algae is actually quite rare but I am curious if you know definitively that you have experienced it in the past. Thanks!
    Dave S. - Forum owner
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    JasonLion's Avatar
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    CYA at 50 typically results in a loss of about 50% of your FC each sunny day, though that can vary quite a bit depending on how much sunlight the pool gets. Higher CYA levels, in the 70 to 80 range, more commonly causes behavior like what you describe.

    You only need to use the mustard algae shock level when you have mustard algae. There is no point in shocking as a preventive measure. If you maintain proper FC levels it is not possible for mustard algae to get started, so just make sure that you don't let FC dip below the minimum.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Butterfly's Avatar
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    Wow, Prov, sounds like you have found the rocking-chair sweet spot for your pool!

    And, yes, as Dave said, I am jealous, too!

    I hope you will keep track of your cl consumption for us and post your results. That would be most interesting and helpful.
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    I'll keep track, and post some results.
    I'm pretty sure we had a bout with mustard algae a week ago. I was away from home and the FC level wasn't maintained correctly....when I got back home, we had powdery growth on the sides and bottom (mostly sides) of the vinyl liner. It was easily brushed and resembled the descriptions I have read online about mustard algae. On the white fiberglass steps, you could easily see a yellow color to it. I shocked at ~15ppm, ran the sand filter 24/7, & brushed frequently. Vacuumed it once, just because...and now it's looking beautiful again. It took almost 4 days start to finish.
    Our pool gets 100% sun, all day. As I mentioned earlier, the water temp (yesterday) was up to 91 degrees. Pretty much a bath. (the kids love it though)

    Prior to shocking the pool to rid the algae growth, I was running CYA at ~25-30 ppm, and adding 1.5 quarts bleach per day to maintain 3-4 ppm FC. The rest of the numbers were pretty much the same as posted, except temp.

    I use a Tayor K-2005 (without the nice high CL test...which I am going to order separately) I cut the sample with bottled water for anything above 5ppm if the test looks too pink to guess well.
    I've been checking the FC level 2-3x daily since Friday, with no apparent drop yet. Since Friday we've had nothing put blazing sun and 100+ ambients.
    I would imagine that when I get home today and check it, it should show some decrease.

    Thanks for the replies, this forum is awesome. I wish I knew about this place last year! I've learned a ton!!
    -Dan

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    Sigh! I'm afraid your optimism (we were all hoping) will be short-lived.

    Dilution from a DPD test is almost never accurate enough to detect the kind of daily loss most experience. It'll take the FAS/DPD chlorine test to reveal your actual loss. We're still hoping, tho!

    Your description does indeed sound like mustard algae. I would suggest VERY careful monitoring of your FC level and, at the first sign of the slightest recurrence, shock heavily and then maintain the mustard algae minimum per chem geek's chart.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Yep, I need the FAS/DPD kit for sure, in fact, I'll call you and order it! (I should've bought the K-2006, but I goofed and bought the K-2005)

    -Edit- I just ordered it through your webpage.......hurry up and ship it

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    Ok, what's the deal here.....
    I got home and not only had my FC level finally dropped to about 4ppm, but there also was a nice surprise on the bottom and sides of the pool. The algae has apparently returned, overnight or during the day today while I was at work. A light coating, not terribly bad....yet?
    We had ambient temp of 108 today, full sun.
    I brushed the entire pool and dumped in 3 gallons of 6% bleach. Probably not enough, but I believe I am wasting my time and money without the better test kit measuring the higher levels of CL.

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    prov,

    Thanks for the order. Our same day shipping cuts off at 2:00pm EDT so we'll have to ship your kit tomorrow. You'll get it Wednesday.

    Meanwhile, 1 small jug of bleach put in your pool each evening until the kit gets there is a good preventative and you won't waste anything.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  12. Back To Top    #12
    Thanks Dave, I'll get this pool chemical stuff figured out and on a real schedule soon enough. The toughest part of this entire learning process is thinking you've got it, and then getting smacked down! At least I don't have a green swamp....I could still see the bottom drain even after I brushed it.

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