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Thread: Where does the algaecide go?

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    Where does the algaecide go?

    I have always used a quat algaecide (Alkyl (50% C14, 40% C12, 10% C16) Dimethyl Benzyl Ammonium Chloride). I usually add some every week. Does it evaporate after a while or where does it go? Does it just build up if it doesnt get used up or what? Is there any side effects to it? I am also curious about the same with a polyquat algaecide.
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    Re: Where does the algaecide go?

    Both types of algaecide get broken down by chlorine, but the Polyquat lasts longer so has a lower chlorine demand as a result. They do not get completely broken down -- the Polyquat gets broken into smaller pieces and these still act like a mild clarifier so will often get caught in the filter if there are particles to capture in the pool while the linear quat (ADBAC) gets split into two but tends to stay in the water so can build up if not diluted. The linear quat is less expensive, but can foam.

    Of course, algaecide is not needed if one maintains the proper Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level as indicated in the Chlorine / CYA Chart.
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    Re: Where does the algaecide go?

    Ok. Thanks for explaining. I have a few bottles of ADBAC that was given to me so I have been just using it. It does foam some when adding it but it usually goes away in about an hour. It has been a very rainy season here and I figure it cant hurt to add it.
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    Re: Where does the algaecide go?

    Quote Originally Posted by easttn
    Ok. Thanks for explaining. I have a few bottles of ADBAC that was given to me so I have been just using it. It does foam some when adding it but it usually goes away in about an hour. It has been a very rainy season here and I figure it cant hurt to add it.

    I think we are just of the mind of why put something like that in your pool if you don't have too? Rain or no it isn't needed to be honest with you.
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    Re: Where does the algaecide go?

    Quote Originally Posted by Brushpup
    I think we are just of the mind of why put something like that in your pool if you don't have too? Rain or no it isn't needed to be honest with you.
    Yes, I understand.
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    Re: Where does the algaecide go?

    If a large excess of linear quat is added to a pool, does it take a large excess of chlorine to break it down and then increase the FAC and TAC? I got black algae when my 35,000 gal colored plaster pool warmed up in the spring. I added $70 worth of Leslie's Black Out trichor and brushed extensively. It only reduced the algae slightly. I then added 152 oz 30% HTH Algae Guard linear quat (ADBAC). Black algae was eliminated and the pool was clear. It then rained 5" and the pool turned cloudy. I keep adding calcium hypochlorite and the chlorine levels will not increase above zero. CYA = 25, CH = 200, TA = 90, pH = 7.6, TDS = 1100, FAC = TAC = Cu = Fe = Pho = Zero
    Thanks from MO City

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    Re: Where does the algaecide go?

    Welcome to TFP!

    I presume you had black algae which is why you used the Black Out Trichlor product. To get rid of black algae, it requires not only exposure to chlorine, but brushing with a heavy brush (wire if plaster; very stiff for other surfaces, but usually black algae shows up in plaster pools). You need to scrape the waxy surface layer from the algae to expose its depths to chlorine. Once you maintain a chlorine level consistently, it shouldn't come back. You said you brushed extensively, but might have needed a different harsher brush head.

    If those measurements are from the pool store, I wouldn't trust them. The CYA seems low.

    As for the ADBAC, it can foam and it breaks down from chlorine faster so you usually notice a higher chlorine demand when using it. What happens to it is that the chlorine breaks it down into an organic without the nitrogen in it and it might get caught in your filter depending on your filter type. 152 ounces of 30% ADBAC (C 12-18) which has typical molecular weight 377.8 g/mole. I don't know the density of what you used, but I'll assume 1.3 g/ml and I'll assume it takes two chlorine to react with the chemical. So 2 * (70.906 g/mole Cl2) * (4495 ml) * (1.3 g/ml) * (1000 mg/g) * 30% / (377.8 g/mole) / (132489 liters) = 5 mg/L or ppm chlorine as a wild guess. It could be more, but not a lot more. So that doesn't sound like very much chlorine demand.

    Did you ever measure a chlorine level since opening the pool? It's possible you had bacteria convert some CYA into ammonia over the winter. However, that will usually show up as CC. Also, your FAC/TAC implies something like a DPD test and realize that those bleach out at high chlorine levels. This is why we recommend you get a proper test kit such as the TFTestkits TF-100. See Test Kits Compared.
    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
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