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Thread: Is this why they sell Algaecide? (dimethyl benzyl...)

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    Is this why they sell Algaecide? (dimethyl benzyl...)

    Soooo I bought some algaecide at the store because I didnt know anything and figured I needed it. But now I've had a revelation.

    Pool chemical companies create 4 steps.
    1.) Balance
    2.) Chlorinate
    3.) Shock
    4.) Algaecide

    Basically the ingredients on step 2 and step 3 are exactly the same for almost every pool company brand, whether it be dichlor, trichlor, cal-hypo.. The shock step is usually sold as a tiny bag with something like 15% higher available chlorine than their step 2 version.

    And I have discovered through reading here that this powdered pool chlorine (Step 2 & 3) stuff will raise your CYA levels to a point where the chlorine is so stable it does not react fast enough to kill off algae, (Where unstable chlorine ... *Clorox liquid style* will react immediately but get destroyed by sunlight and have no long lasting effects).
    And because as the chlorine dissolves and gets used up, the CYA still remains to make your next CYA added chlorine "Ultra Stable"... or Over-Stable... And thus, the law of diminishing returns starts to kick in.

    Sooo.. They have a 4th step. Another chemical that is not chlorine designed to kill algae that is not effected by CYA levels. Typically this is dimethly benzyl ammonium chloride.
    Because the pool chemical companies know their chlorine will build up CYA so high, they need yet another product to kill algae blooms which grow faster than a super stable chlorine can kill it.

    And thus, if you maintain a proper CYA level, (Around 30-60 depending on direct sunlight on the pool correct?) your regular liquid chlorine bleach will have no problem killing off algae and you will not need a special algaecide like dimethly benzyl ammonium chloride at all.

    How am I doing Chem Geek? Can I return my Algaecide?
    16,000 gal in-ground
    Pump: Hayward C48K2N143 1HP 230V
    Filter: DE Triton Nautilus FNS-36

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    Doing great

    Chlorine is chlorine, it doesn't matter where it comes from. What does matter is what other chemicals are included in with the chlorine and if you want them or not.

    Several of the common algaecides have unpleasant side effects. There is no reason to use algaecide day to day, but there are occasional special situations where having an algaecide is worth it (AA treatments for example).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Mod Squad Patrick_B's Avatar
    Join Date
    Jun 2011

    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    Very concise boon. Excellent post, anf welcome to TPF. Looks like you've seen the light.

    I would certainly say take it back....highly doubtful you'll need it. Let us know what they say.
    TFP Moderator
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    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    Quote Originally Posted by Brushpup
    Very concise boon. Excellent post, anf welcome to TPF. Looks like you've seen the light.

    I would certainly say take it back....highly doubtful you'll need it. Let us know what they say.
    It was actually from Sam's Club.. It wasn't very expensive either so I might keep in in case I need it for some reason.... As I await my test kit and pool cover to come I'm dealing with an algae issue that I'm fighting blind (Is this futile?). My pool was opened with 5lbs of cal-hypo (And some algaecide) a week ago, and the previous owners used cal-hypo exclusively (They had a 25lb bucket of it anyways), so my CYA may currently be through the roof, which explains why I have not been able to get the green fog out of my water.. I can see the bottom now but its not getting past a "point". I actually added some algaecide today because I figured my CYA was probably extremely high and preventing the chlorine from working as fast as it needs to. Last night I added 1.4 gallons of liquid chlorine and another gallon this morning.

    My PH is probably crazy so I'm picking up some muriatic acid, borax and baking soda today for controlling that once my test kit arrives.

    My DE filter is out for repair so my water will stay cloudy (currently on recirc), but hopefully it will turn into a grey / white dead cloud so the DE filter will just suck up all the dead stuff when I add it back to the system... And then I'll be crystal clear... Followed by a scrubbing of the walls, steps and ladder..

    ... Whew... Pools are hard work!! But hopefully "trouble free" soon
    My test kit will eliminate a lot of the guess work when it comes... For now I'm taking a water sample to the pool company.
    16,000 gal in-ground
    Pump: Hayward C48K2N143 1HP 230V
    Filter: DE Triton Nautilus FNS-36

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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    We generally don't recommend that kind of algaecide as it is inexpensive, it can foam and isn't very effective or long lasting, compared to the more equipensive Polyquat 60 algaecide which is the type we do recommend - and even then only in certain situations. Algaecide is more of a preventative rather than a treatment for an algae bloom.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    Basically, you've got this analysis correct though the "algaecide" is often one of a variety of different products promoted to prevent algae. It's not only the linear quat you mention, but Polyquat, copper ions, and phosphate removers. So yes, return your algaecide, especially since it's not Polyquat which is the only one you might use on occasion such as during an ascorbic acid treatment for metal stains or during winter closure of your pool.
    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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    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    Hi Boon,

    Like you I bought a pool that already came with very high CYA levels. I have been doing weekly water replacements to try to bring it down. I sometimes get frustrated and think it's to hard but when I play in it with my 4 year old it's totally worth it.

    Mixing the reagents to do your daily pH or chlorine addition is a pain. The sooner you order your automatic stirrer the faster you'll get it!!!

    Congrats on figuring out the cycle!! Sinister... isn't it?

    17,000 gal plaster with spa. Pentair Clean & Clear cartridge filters. Jandy systems with Aqualink RS and Polaris 360.

    Pool Store free since May 2011!

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    dorpo75's Avatar
    Join Date
    Jul 2009
    NE Ohio

    Re: Is this why they sell Algaecide? (dimethyl benzyl...)

    I think the initial post here ought to be a sticky. It spells out the evil cycle in plain terms and makes even the most noobiest of noobs able to understand what is happening in their water. Great information in a precise easy to read post.
    2005 Dimension One Venture model 370 gal. hot tub. We'll be using the TFP method to keep it clean and ready to use!
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