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Thread: Best time to add algaecide, day or night?

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    In the Industry

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    Apr 2009

    Best time to add algaecide, day or night?

    I say during the day as that is when it's blooming, but does the scientific data back that up?

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    JasonLion's Avatar
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    May 2007
    Silver Spring, MD

    Re: Best time to add algaecide, day or night?

    We don't recommend using normal algaecide at all, except for a couple of special cases like the ascorbic acid treatment and winterizing. We do often recommend borates, though not generally because of their algae killing.

    When you are using algaecide, there are two different ways they can work. Some, like polyquat and linear quats, get used up as they kill algae. Others, like borates and copper, stay in the water and continue killing algae over long periods of time.

    The first kind, that gets used up, is not very effective against live algae. The algae keeps growing and you run out of algaecide. If you were to try this you would want to add the algaecide at night, to give the algaecide the best chance of working before too much new algae grows and uses it up.

    The second kind, that remains in the water and continues killing algae, works all the time so it doesn't matter when you add it.
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  3. Back To Top    #3

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    Apr 2009

    Re: Best time to add algaecide, day or night?

    Ok, let me rephrase the question.
    When is algae most vulnerable to be killed? by whatever means. Day or night? Or does it matter at all?
    I've heard some say it is best to catch it in the day when it's in full bloom. Others say at night when it's more dormant. What is their reasoning?

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    Re: Best time to add algaecide, day or night?

    It depends a lot on WHAT you are killing the algae with. If you are using an ammonia based 'chlorine enhancer' like Green to Clean or Yellow Out then these kill algae because they form monochloramine in the water and the algae consume it as a food source and die. Daytime when they are feeding is going to be more effective.
    If you are taking about linear quats and polyquat, these work by disrupting the cell membrane so it really doesn't matter that much. However, they also make the algae more vulnerable to chlorine so adding the algaecide during the day and then shocking at night so there is less effect on the chlorine from UV might be more effective.
    If you are talking about bromide based algaecides they work by taking the CYA 'out of the loop' in an overstabilzied pool by converting it to a bromine pool. (United Chemica's products and many of Proteam's products fall into this category). They are most useful when the algae is from overstabilization but are a band-aid rather than a cure! Once again, at night would be better since bromine cannot be protected from loss by UV light.
    Borates are more of an algaestat rather than an algaecide. They are dosed to 50 ppm (80 ppm for biguanide pools) and maintained there, not only for their algaestatic effects but also for their pH buffering and water softening and clarifying effects.

    Copper is a poison that is the only thing in this group that can kill algae without chlorine or bromine present, so time of day really does not matter. However, it's disadvantages far outweigh it's benefits so it is not really recommended in the vast majority of cases. Manufacturers LOVE to push their copper based algaecide because it's one of the cheapest for them to make (some copper sulfate and some EDTA...both cheap chemicals!) while Polyquat is bought from Buckman Labs (they own the patents) so the profits are not as high.

    However Polyquat 60 (why ANYONE would buy Polyquat 30 is beyond me once you work out the cost per dose!) is a very effective algae inhibitor, especially at the beginning of overstabilization or during a stain removal treatment with citric or ascorbic acid (which create a hugh chlorine demand for a few days and shocking is not an options if you don't want stains back). Linear quats are not long lasting and have a lot of side effects such as foaming and stinging eyes

    Halogens (chlorine and bromine) are actually the most effective algaecides we have if you are maintaining proper water balance, once a pool gets algae. (Granular trichlor can be useful in cases of black spot algae as can copper under certain conditions but in most cases chlorine, a steel algae brush, and patience and elbow grease will take care of it...remember, black spot indicates a pool that was ignored or out of whack for an extended period of time, often months, so it's the hardest type to eradicate and can take a while!)

    If the pool is sanitized with biguanide then the choice of algaecides is basically limited to linear quats and borates. The second are a better choice, IMHO.

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