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Thread: Killing Algae and maintaining pool balance

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    Killing Algae and maintaining pool balance

    Hello,

    I really screwed up my pool last year and I am paying the price this season. I have quite a bit of algae that I am trying to kill while keeping my CSI negative to help with a scaling problem from last year.

    Is it ok to add muriatic acid to the pool while in the process of shocking to kill algae?

    25,000 Gallons
    PH 7.5
    FC 5+ (test kit limitation)
    TA 120
    CH 430 (Fill water is at 400 ppm)
    CYA 35
    Temp 70 Deg.
    CSI 0.15

    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorinator, 1.5" pvc schedule 40 throughout, Leslies copper therm 260,000 bt/h pool heater

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

    Thank You,
    Bill
    25,000 Gallon
    Vinyl Liner
    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorine feeder, 1.5" pvc schedule 40 throughout, Leslies coppertherm 260,000 btu/h pool heater, Dolphin Diagnostic robot.

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

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    Re: Killing Algae and maintaining pool balance

    Hi, Bill,

    Welcome to the forum.

    Is it ok to add muriatic acid to the pool while in the process of shocking to kill algae?
    No problemo
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Killing Algae and maintaining pool balance

    Thank you.

    I am apparently having an acid demand problem as well. The acid demand test took 30 drops to lower the PH from 7.5 to 7.2 and I don't believe that the volume of acid generated by the the pool calculator is high enough given the results of the acid demand test.

    I am going to periodically add muriatic acid in small quantities until i get the desired results. Is this the right course of action?

    According to the acid demand test I would need 5.37 gallons of acid to lower my PH is this the correct amount to add over time?
    25,000 Gallon
    Vinyl Liner
    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorine feeder, 1.5" pvc schedule 40 throughout, Leslies coppertherm 260,000 btu/h pool heater, Dolphin Diagnostic robot.

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

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    Re: Killing Algae and maintaining pool balance

    Bill,

    As a general rule, we don't use the acid demand test for much.

    I am not familiar with it (someone will be along soon who is) .

    Something is very wrong in the calculation, however. Far less than that is needed to lower your pH from 7.5 to 7.2. I have not calced it but I would guess between a quart and a half gallon.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    Re: Killing Algae and maintaining pool balance

    It would be nice if you could put the basic specs of your pool into your signature. That makes it easier for us to help you.

    I calculate that you will need about 6 cups of acid, if your PH and TA readings are correct.

    If your FC level is high enough the PH test might be reading incorrectly, which could dramatically throw off the acid demand test. That is the problem with adding acid while shocking, the PH test doesn't work at high FC levels.
    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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    Re: Killing Algae and maintaining pool balance

    Thanks for the information guys!
    25,000 Gallon
    Vinyl Liner
    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorine feeder, 1.5" pvc schedule 40 throughout, Leslies coppertherm 260,000 btu/h pool heater, Dolphin Diagnostic robot.

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

  7. Back To Top    #7
    Guest

    Re: Killing Algae and maintaining pool balance

    You might not have an acid demand problem. Are you testing the pH with the chlorine at shock level? High chlorine levels will interfere with the pH test and make it read higher than it really is.
    (also algae will be killed more effectively at a higher pH than an lower one because the higher pH will favor the formation of monochloramine 7.8 to 8.0 is the most effective so I don't understand why you want to drop your pH to 7.2).

    Wait until you chlorine levels drop back to normal and THEN test your pH.

  8. Back To Top    #8

    Re: Killing Algae and maintaining pool balance

    Is this statement not true then?

    http://www.edstrom.com/DocLib/MI4148.pdf

    Disinfectant Strength Comparison

    The germicidal strength of different forms of chlorine in water are ranked as follows:

    HOCl > OCl– > inorganic chloramines > organic chloramines

    HOCl is 100 times more powerful an oxidant and disinfectant than is the hypochlorite ion.
    Consequently, free chlorine is most effective at a pH of 5 to 7 where HOCl is the predominant
    form. The effectiveness declines with increased pH.
    25,000 Gallon
    Vinyl Liner
    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorine feeder, 1.5" pvc schedule 40 throughout, Leslies coppertherm 260,000 btu/h pool heater, Dolphin Diagnostic robot.

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

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    JasonLion's Avatar
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    Re: Killing Algae and maintaining pool balance

    Quote Originally Posted by Shark0311
    Is this statement not true then?
    That article does not cover what happens when there is CYA in the water. They are assuming no CYA. CYA changes things significantly. You can look at this post for more information.

    There are also some interesting, but more complex, chemical reactions that can happen with or without CYA when PH is higher that can kill algae, which are outside the scope of that article. For example, chlorine can react with algae to form monochloramine, which can then kill more algae.
    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

  10. Back To Top    #10

    Re: Killing Algae and maintaining pool balance

    Thanks for the information!
    25,000 Gallon
    Vinyl Liner
    Equipment: 1.5 hp generic pump, 225 lb sand filter, Hayward 8lb inline chlorine feeder, 1.5" pvc schedule 40 throughout, Leslies coppertherm 260,000 btu/h pool heater, Dolphin Diagnostic robot.

    Location: Western Suburbs of Chicago w/ exposure to lots of sunlight.

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