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Thread: CYA over 100 with yellow/mustard algae

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    Default CYA over 100 with yellow/mustard algae

    Hi, and thanks for the great forum. I've been reading for several weeks and finally decided to register and ask a question.

    I recently converted to BBB after 7-8 years of using stupidly-expensive BioGuard shock and smartsticks. As a result, my CYA is quite high... dip sticks read right at 100; the pool store tested at 91; and my recently-acquired Taylor K2006 kit reads well over 100.

    I immediately took the FC up to about 10, and I'm losing about 2ppm per day, but it holds fine overnight. I had been keeping it in the 3-5 range previously.

    The water looks fine, except that I have a recurring problem with what I think is the dreaded yellow/mustard algae. I've had a minor problem with this for 2-3 years in late summer. It appears on all flat surfaces and the wall of the shady side. It's a very fine brown/yellow dust that - when brushed - "poofs" into a cloud that looks brown/yellow/greenish, but very quickly disappears. Then, 2-3 days later, it's back on all flat surfaces and the shady walls, and other places with poor circulation.

    All this time, I convinced myself it was just some fine dirt or pollen that wasn't being filtered by my cartridge filter. But after reading extensively here, I'm convinced it is the hard-to-kill yellow/mustard beast. I can't imagine that dirt would attach itself to vertical surfaces. There's not a ton of the stuff (very spotty), and it does go away with cooler weather.

    Problem is: with my CYA so high, I would need to add an insane amount of bleach to kill this stuff. The best guess chart says 75-100 ppm of FC. Are you guys really recommending that??

    I have a cartridge filter, so I get very little (if any) water loss in the normal course of operating the pool. This is probably why the CYA has built up so high. But also, I have no way to vacuum the stuff to waste. It's an IG gunite pool, but I'm not too comfortable with taking half the water out.

    I would welcome any and all suggestions. Thanks. I listed my equipment and other test results below.

    35X20 (approx), IG gunite, 18k gal, pebbletec plaster
    Pentair cartridge filter, 2.0 HP pump

    FC=10
    CC=0
    CYA=>100
    pH=7.6
    TA=105
    Borates=40

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    Default Re: CYA over 100 with yellow/mustard algae

    1. Do a dilution test with the CYA, to determine your actual level. Mix 1/2 cup tap water (or distilled) with 1/2 cup pool water, and run the CYA test against that mixture. Multiply the result x2.

    2. If you actually already have 40 ppm of borates (how did you test?) go ahead and take the level up to the 60 ppm effective level. On your pool, that would mean about 7 more boxes of borax and about 2 gallons of muriatic acid.

    3. Your PF (PoolFactor) is about 6. A gallon of 8.25% bleach contains about 0.7 lbs of chlorine. So, each gallon will add about 6 x 0.7 or 4 ppm of chlorine to your pool. Three gallons will add 12 ppm. That will get you to 20 ppm. Get there, and keep it there for awhile.

    4. Get a cheap OTO (yellow / red drops) kit locally. Use it the next time your test your pool. It will turn very dark yellow to orange --learn to use it to get a guesstimate of your high chlorine level, without using the DPD - FAS test every time.

    5. Brush your pool at least 3x per week, each time AFTER dosing with chlorine.

    6. Try all that for a week. If you don't see an improvement, add another 4 boxes of borax, another gallon of acid, and take your chlorine levels up to 30 ppm.

    You CAN swim at FC=30 ppm when CYA > 100 ppm, with no ill effects on people. We're not quite sure what those levels do to women's fashion swimwear, so leave the $120 swimsuits in the house. . . unless they are old.

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    Default Re: CYA over 100 with yellow/mustard algae

    Hi Ben. Thanks so much for the detailed response.

    1. I did the CYA dilution test, as you suggested, and it did come in a little lower at 80. I also re-ran the regular non-diluted test and it was still over 100, but a little less than before. As I said, the pool store said I'm at 91; and the strips, while hard to read, seem to be dead-on at 100. In any case, my CYA seems to be somewhere in the range of 80-100.

    2. Regarding borates, I have the LaMotte strips, which seem to be right between 30 and 50. Also, the pool store said I was at 29, and that was right before I added 2 boxes of borax, which should have taken me above 40. Are you sure I need 7 boxes of borax to go from 40 to 60ppm in 18kgal? According to the bleachcalc.exe, 7 boxes of 76oz borax (532 oz) would increase borate ppm by 90. I do recall reading here that the bleachcalc app might be inaccurate for borax. Just want to make sure before I dump that much borax in the pool.

    3. I'll take the chlorine to 20ppm tomorrow after a trip to Wal-Mart to restock. Are you sure 20-30ppm is going to be high enough to kill this beast? From what I've read here, others have gone much higher (35-40 for 7+ days), and they had much lower CYA than me.

    4. I'll get the OTO kit tomorrow also. I wasn't looking forward to counting 100+ drops in the DPD test.

    I'll brush the pool regularly and update back here with any improvement. One question: because I have a cartridge filter, I can't vacuum this algae to waste. My pool store rents a portable pump for this purpose. Is that something I should consider also? Losing some water might also help drop the CYA a bit. Or should a cartridge filter trap this stuff? Do I need to clean the filters during this process?

    Thanks again for the detailed response.
    __________________________________________________
    35X20 in-ground gunite, free-form, 18k gal, pebbletec plaster, Pentair cartridge filter, Pentair 1.0 HP WhisperFlo pump, Polaris 280, heater, waterfall, Taylor K2006 kit and K1106

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    Default Re: CYA over 100 with yellow/mustard algae

    You've already added 2 boxes, so deduct those, but yes, 7 boxes was what I intended. Bleachcalc has an error in the borate calculator. Feel free to work up to 60 ppm in 2 box doses, if you prefer.

    FC = 20 won't necessarily kill it, but it will likely stop it. Mustard algae doesn't take over the pool suddenly, so if you get to 20 ppm, and brush, and still see it recurring -- add more.

    When testing, use the 10ml sample size, rather than 25ml sample, At 10 ml, 20 ppm = 40 drops, not 100.

    A cartridge filter will normally trap dead - but not live -- algae.

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    Default Re: CYA over 100 with yellow/mustard algae

    Update... I took the borates up somewhere north of 50 (not sure exact level), and I held the FC at 20ppm for last 10 days. I've been brushing almost every day and also set the Polaris to run 6 hours per day. The filter pump is running 24/7.

    No sign of algae anywhere. But I'm guessing that could be due to the excessive brushing and Polaris run-time. So, as of yesterday, I'm letting the FC come back down to 8-10 and I'll stop brushing for a couple days to see what happens. I also reset the filter pump and Polaris to normal run times (12 and 2 hours respectively).

    So far, so good. We've been swimming with no ill-effects at 20ppm, and the water looks fantastic.

    Thanks for all the help. If the algae returns, I'll update again.

    By the way, any suggestions on how to get the CYA down to a more normal level? I think I'd like to keep it around 50-60.

    Mike
    __________________________________________________
    35X20 in-ground gunite, free-form, 18k gal, pebbletec plaster, Pentair cartridge filter, Pentair 1.0 HP WhisperFlo pump, Polaris 280, heater, waterfall, Taylor K2006 kit and K1106

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    Default Re: CYA over 100 with yellow/mustard algae

    With a cartridge filter, you won't be losing much water on backwash. So, CYA levels won't drop on their own.

    To go from CYA=100 to CYA=50, you'll need to dump 1/2 of your pool, and refill. The only other way is to allow the pool to get 'slimed' over the winter. CYA usually bio-degrades, to nitrogen gas (no problem) or nitrates (usually not a problem). But sometimes, it biodegrades to ammonia, which is a big problem. So, that's not really recommended.

    If you do drain, be SURE to do so ONLY when the ground is reasonably dry. Even concrete pools will float out of the ground when emptied, if the ground water levels is high enough.

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    Default Re: CYA over 100 with yellow/mustard algae

    Thanks Ben. I'm not at all inclined to drain half the pool due to risk of floating and cost of the water. I'm even less inclined to "slime" the pool over the winter.

    So, I've begun to think maybe I'll just keep the CYA high and maintain FC levels accordingly high as well. I've read here about some of the benefits of that approach. The one significant downside seems to be that if you slip-up and get an algae bloom, it takes an enormous amount of chlorine to kill it.

    One question: my daily chlorine loss is right at 2.2 to 2.3 ppm (after two weeks of careful tracking). That strikes me as a little high. Is that normal with CYA>100? What would my daily usage be at CYA=50-60? I'm in North Texas and my pool gets 7-8 hours of direct sun per day. Water temps range from 84-92 in the summer. Thanks again.

    Mike
    __________________________________________________
    35X20 in-ground gunite, free-form, 18k gal, pebbletec plaster, Pentair cartridge filter, Pentair 1.0 HP WhisperFlo pump, Polaris 280, heater, waterfall, Taylor K2006 kit and K1106

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    Default Re: CYA over 100 with yellow/mustard algae

    At 100 ppm CYA, typical FC loss is around 15%, but you are at 20 ppm so you're doing even better than the predicted 3 ppm loss. If you didn't have yellow/mustard algae, your minimum FC would be more like 7.5 ppm in which case you'd only be losing around 1.2 ppm FC per day which is lower than the typical pool (2 ppm is fairly typical; 3 ppm is not uncommon).

    You should check behind light niches and under removable ladders. Yellow/mustard algae prefers shades and often hangs out in areas with poor water circulation. You need to completely kill it or else it will come back when you let the FC level drop below roughly 15% of the CYA level.
    15.5'x32' rectangle 16K gal IG concrete pool; 12.5% chlorinating liquid by hand; Jandy CL340 cartridge filter; Pentair Intelliflo VF pump; 8hrs; Taylor K-2006 and TFTestkits TF-100; utility water; summer: automatic; winter: automatic; ; PF:7.5

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    Default Re: CYA over 100 with yellow/mustard algae

    Thanks to all. This is such great information. I've owned 3 different pools over the last 13 years, and for the first time, I actually feel like I'm in control, and know what I'm doing, and why.

    For the last 4-5 days, I've been letting the FC come down to 8, then add 1 gal of 8.25% bleach to get back to 12, then 2 days later I'm at 7.5-8.0. At those FC levels and with CYA>=100, I should be losing around 1.5ppm per day, using chem geek's 15% typical figure.

    Since I'm higher than that (2.2-2.3 ppm loss per day), I assume I'm still fighting something in the water, most likely the yellow/mustard algae. But I've checked everywhere and see no sign of algae anywhere. I'll keep checking. My filter pressure is up about 4 PSI over this 2-week timeperiod, so I hope that's the dead algae. I'll clean it out this weekend. Hope I haven't declared victory too soon.

    I suppose it's also possible that my higher daily usage could result from the extreme heat and sun we've had over the last week (temps over 100 and no clouds in sight). Bathing load has been light. I'll keep monitoring. 1.2-1.5 sounds very good to me.

    Bottom line, I'm starting to like the idea of high CYA... higher FC levels, lower daily consumption, and less frequent manual additions of bleach. Just need to make sure I've killed this yellow beast for good.

    Thanks again for all the information and advice.

    Mike
    __________________________________________________
    35X20 in-ground gunite, free-form, 18k gal, pebbletec plaster, Pentair cartridge filter, Pentair 1.0 HP WhisperFlo pump, Polaris 280, heater, waterfall, Taylor K2006 kit and K1106

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