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Thread: Black Algae Experiment

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    Black Algae Experiment

    I had just posted or thought I did a question,guess not. Anyway new here.

    Inground pool owner for 12 years, plaster 20 k. Ok here goes. I have not had much luck with a bottom of balck algae. Not to much on the sides. I called a pro and wanted a price for a acid wash. WHoaaa!!! 1500.00 bucks, not today thank you. So I looked for alternatives knowing well that it might also etch the plaster badly but no alternative.

    So, I have heard of using a citric acid with a full pool for two days and of course brushing the livin bejesus out of it. So I called another pro pool store and a few days later they called. I had left a message of my address and pool size etc etc. The person had google earthed my house and pool and looked at the size and type of pool.???

    Anyway we talked about the pump brand ,filter brand and models, pool equipment and such. Waht we were looking for were metals that might get scarred by the acid he suggested. So this pool does not have but a light ring at the deep end and no ladders or other metals. The pump and filter passed the acid test with him.

    One thing that I had learned was wash your de filter with degreasser before doing what he was telling me ,reason,,,, the oils embed from the muriatic acid into the filter and renders it useless in spots, he was suggesting after calculating gallons of pool and how much muriatic acid (15 gallons) to use while the pool will still be full with circulating at the same time. We also calculated how much baking soda (36 lbs)to have on hand to stop the muriatic acid process. The safety regs for us humans also.

    I can ballance water with my eyes closed so not a problem with this pool. My question is has anyone ever heard of this being done?

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Black Algae Experiment

    Welcome to TFP!

    There is so much baloney in what you were told, I hardly know where to begin. Citric acid would be used for metal stains, not for black algae, and ascorbic acid is better than citric acid for metal stains anyway. Muriatic acid would be used if you were going to to your own acid wash, but I would not recommend that. The guy was right about not adding acid to your filter before degreasing it, though that is usually more relevant when cleaning a cartridge filter.

    For getting rid of black algae you want to use elevated chlorine levels (see SLAM- Shock Level and Maintain) and brushing with a strong brush (presuming you have a plaster surface) since you want to scrape off the waxy surface layer to expose the algae below to the higher chlorine levels to kill it.

    To get black algae, your active chlorine level must have been too low for a long time. I suspect your Cyanuric Acid (CYA) level is high so before doing an SLAM you may want to do a partial drain/refill to lower the CYA level since that will let you use a lower chlorine level for the SLAM. Get yourself a proper test kit immediately (see Test Kits Compared) and then tell us your accurate test results.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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