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Thread: Algae growth, pool gallons and bleach

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    Algae growth, pool gallons and bleach

    Alright I just bought a house with a pool here in sunny arizona. I had the pool under control until the summer UV rays started beating down on it. The pool has turned cloudy and a greenish color. I know its a build up in algae.

    The pool itself is not a perfect square or square its in the shape of a human kidney is as close as I can describe it. I calculated the pool to contain 21,100 gallons of water. I was wonering if that sounded right considering the infrmation below.

    Length: 35 feet
    Width: (largest part) 16 feet
    Shallow end: 3 feet
    Deep end: 8 feet

    Now I realized it has algae growth due to the increase in UV light allowing it to grow and I didn't increase chlorine. So now the pool is a tealish light green and in the deepend its quite cloudy, I can barely see the skimmer 8 feet down. I know I can use a "shock" but what I have been reading on the internet is they are expensive and don't need to be used.

    The Total Chlorine is at about 2ppm.
    Free cholorine is low at about 0.5.
    The PH is high at about 8 but I already put in 32oz of muriatic acid about 4 hours ago then another 16oz about an hour ago as the pH before was at about 8.4 before.
    Total Alkalinity is high at about 150 ppm.
    Cyanuric Acid is high at about 300ppm. (I know I need to empty to pool but thats for another day)

    I have about 5 "3 inch tabs" in the floater and I put 3 on the floor of the pool this morning. One per a section.

    I read that cheap household bleach can kill the algae. So based off of my 21,100 gallon pool I am wondering how much bleach do I need?

  2. Back To Top    #2
    poolgirl22's Avatar
    Join Date
    Apr 2010
    Stephens City, VA

    Re: Algae growth, pool gallons and bleach

    Edited to add a warm welcome to the friendliest pool site on the internet!
    I'm going to take a stab at this one...more knowledgeable and experienced folks will be along shortly. But, the first item of business will likely be the high CYA level you indicated. At that level, the amount of chlorine needed to appropriately treat your pool and bring it to sparkling beauty is very very high.
    You will likely be advised to replace a great quantity of your water. 2ppm of chlorine is not enough with a CYA of 300 to keep algae at bay. I would stop using any trichlor pucks, powdered 'shock' products, etc and stock up on regular unscented bleach or liquid chlorine. The bleach should read 6% sodium hypochlorite and the liquid chlorine/shock should read 10% or 12%.

    In the interim period of waiting for specific advice, please read pool school which is linked in the upper right corner of every page.

    Read pool school again, and again, and again, until it is firmly embedded in your mind.
    Gather the specifics of your pool and add them to the signature line via the control panel in the upper left corner. It helps us know what you have so help is a little more tailored to your needs.

    Order a test kit recommended by this site. I have the TF100 as do many others here. In pool school there is a section on test kits and compares them.

    Check out and learn how to use the pool calculator which is linked in my signature. This is where you will be able to put in your current tested levels and your goal levels based on your pool's profile. It will tell you how much of what to add to do different things. Once you use pool calculator successfully you are free of the pool store.

    Above all, rest assured you are in good hands here. No one has any agenda to sell products you don't need and everyone has been in your shoes...some of us just 3 weeks ago...
    Backyard pool-less, but used to be.....
    16,100 gallon, 18x38 3.5 ft deep oval AG, Vinyl, Sand, 1hp pump Liquidator TFT100 test kit

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    Re: Algae growth, pool gallons and bleach

    Thanks for the reply! Thanks for the welcome too! Gotta love internet forums

    Yeah I am in the middle of finals right now so I can't spend that much time on the pool. lol

    Using the calculator I determined I need 89 oz of bleach. Which I just put 96oz in. Ill see if it clears up in the next 2 days. I put an umbrella over the deep end to try to limit the uv light thats hitting the water.

    I just filed with the city to get a permit to empty my pool. Ill probably do it next week on Thursday or something. gotta skateboard it too!!!!
    i'll post my results soon.

  4. Back To Top    #4
    poolgirl22's Avatar
    Join Date
    Apr 2010
    Stephens City, VA

    Re: Algae growth, pool gallons and bleach

    Be sure with the pool calculator you are setting up the values in the suggested goal will then tell you in the top part of each section what your target ranges are...
    Putting in the info from your first post I'm getting a free chlorine minimum of 23 and a max of 33 based on that CYA of 300...the biggest challenge with your situation is the's just too high and pool school will explain why.

    Good luck with finals and please gather the info I outlined so when your exams are done you can get to enjoying that pool.

    I'm hoping one of the experts will come by soon....
    Backyard pool-less, but used to be.....
    16,100 gallon, 18x38 3.5 ft deep oval AG, Vinyl, Sand, 1hp pump Liquidator TFT100 test kit

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    Mod Squad zea3's Avatar
    Join Date
    Jul 2009
    Houston, Texas

    Re: Algae growth, pool gallons and bleach

    First off, welcome to TFP! Second, what are you using to test your water? It is very important to know what your CYA level is so that you can shock the pool to kill the algae. With 300 CYA your regular FC target is 23 to 33, and shock level is 58. To raise FC to shock level you need 13 96 ounce bottles of bleach. You would need to keep the FC as close to shock level as possible by testing and adding bleach for as many days as it takes to kill all the algae and pass the overnight test. That is a whole lot of bleach! If draining is not an option, look into reverse osmosis treatment for the pool.
    TFP Moderator
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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Algae growth, pool gallons and bleach

    Also please note that you don't just dump a bunch of chlorine in and walk away expecting the pool to clear. It doesn't work that way. With an algae bloom, chlorine is consumed rather quickly at first so you may need to add more even in the first hour or two after adding it. After the first day, you may not need to add it as often, but the key is to maintain a high FC level. However, with your high CYA level, it will take a lot of chlorine to get to a high FC level.

    With a CYA level as high as you have, I'd just start diluting the water as it's going to take a lot of dilution to get to 80 ppm which might be where the CYA level needs to be for sunny Arizona.
    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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    frustratedpoolmom's Avatar
    Join Date
    May 2007
    SWSuburban Chicago, IL

    Re: Algae growth, pool gallons and bleach

    Quote Originally Posted by matt.rubin
    I just filed with the city to get a permit to empty my pool.
    Good thing, cuz that's about your only option!

    Welcome to the forum
    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
    Perfectly Clear Pool Service, Find me on Facebook!

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    Re: Algae growth, pool gallons and bleach

    ALright so emptying the pool. I hear it takes all day.

    I know the pool pump I have has a backwash system. I can use it to lower to the water level. I have used it to lower the level when it rained, twice. I am not sure if it goes to a sewer output but I assume it does. How are backwash systems normally hooked up?

    I wont be able to empty the pool till Thursday. I hear it takes pretty much all day and you must start super early. I believe I can rent to pump for 32 bucks at leslies.

    Anyway can the backwash system be used to empty the entire pool or do I have to go rent a pump?

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    Join Date
    Jan 2009
    Cupertino, CA

    Re: Algae growth, pool gallons and bleach

    If it takes a permit to empty the pool, most likely they will want it dumped into the sewer, not on the ground or street/storm drain. It's unlikely your backwash setup does that, so you'd want a separate pump. Or maybe two. Find out the GPM for the pump you're thinking about, and figure out how long it will take. (I have a little 6 GPM sump pump and that would take about 60 hours to drain your pool. I think you would want something with a bit more oomph.)

    Incidentally, I'm curious how you came up with the CYA 300 number.
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
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    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    SouthWest Alabama

    Re: Algae growth, pool gallons and bleach

    Since you stated you're in Arizona I'll take a different tack.
    First Welcome to TFP

    How are you planning to refill the pool?
    However it is have the fill water tested befrore you put it in the pool. Being in Az your fill water is known for being hard.
    Having said that if your fill water is hard you might want to consider contacting one of the companies that treat your pool water through Reverse Osmosis. You won't have to drain the pool and it'll bring the CYA as well as the CH (calcium Hardness) down.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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