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Thread: Please help with green algae problem.

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    Please help with green algae problem.


    Thanks in advance to all who respond. The TFP website and forum have been tremendously helpful for me.

    I have a small problem.

    I converted to the BBB method a few weeks ago. Prior to that I was using stabilized chlorine pucks with an inline chlorinator. My CYA levels were off the charts and the water was cloudy and acidic. It took a long time with partial drain and fills, but I finally got the CYA number down to a reasonable level. My pool is small - the pool store has it on record as 6400 gallons, but I calculated closer to 5000.

    I bought a TF-100 and have been testing regularly. The CYA level is 70 (I have tested on several occasions to make sure I was reading the turbidity test correctly, and I always get around 70).

    I treated my pool once with a couple cups of borax to raise the pH to the correct range, and it has been rock steady at about 7.4-7.5. I added about a pound of baking soda, and my TA has been very steady at 90-100.

    I have tested my free chlorine with the DPD test every night. It has never been below 5.5. I add bleach either at night or early in the morning (usually takes between 2-4 cups depending on sunlight). CC is 0.5 (maybe not even that as the water barely turns pinkish when I add the second reagent).

    Test results from tonight: pH 7.5, T.A. 90, FC 6, CC 0-0.5, CYA 70

    Today I noticed a small growth of green algae on the steps in the shallow end and a few spots of green algae in the corners of the pool in the deep end. The water is also not as clear as when I first converted to BBB. I thought if I maintained FC levels of 5% of the CYA level that algae should not be a problem?

    I added more bleach than usual tonight. I guess I need to shock it now? Anything else I should change or adjust?


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    Mod Squad zea3's Avatar
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    Jul 2009
    Houston, Texas

    Re: Please help with green algae problem.

    According to The Pool Calculator, for a CYA of 70, your normal FC range is 5-10 ppm. By staying at the low end of the range, you likely drop below 5ppm during the day and as a result are beginning to have an algae bloom in the areas of the pool that typically have poor circulation. Go ahead and take the pool through the shock process, taking care to brush the pool well. After completing the shock process use 10 ppm as your target and you should not have anymore difficulties with algae.

    Edit: You did not mention a CA test result, is this a vinyl liner pool?
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  3. Back To Top    #3

    Re: Please help with green algae problem.

    It is fiberglass.

    I have not done the calcium hardness test yet.

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