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Thread: Black Algae - can/should i use polyquat when shocking?

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    busbeepbeep's Avatar
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    Black Algae - can/should i use polyquat when shocking?

    I just spent a couple of hours swimming in the pool scrubbing black algae off the walls using a trichlor puck and a SS brush. I managed to get a lot of it to break off wherever it was protruding from the wall, but there is a lot remaining. Lots of pits and grooves in the plaster (~ 25 yrs old).

    I'm pretty positive it is black algae. The spots are round, and they smeared dark green when rubbing off.

    What should be my shock level to try to get rid of this black algae from ****? I have a bottle of Polyquat 60. Will that help? I read it can help break down the chlorine resistant parts of the algae.

    Any suggestions?

    Test Results:

    FC 5
    CC 0
    TA 80
    PH 7.4
    CH 500
    CYA 25
    Borates : hopefully 50ish, added yesterday, didn't try test strip yet.

    Besides the black spots, the water looks better than ever.
    17,000 gallon in-ground plaster (circa 1985) | Tagelus 60 Sand Filter | Whisperflo WFE-3 3/4 hp (1.25HP/1.67SF) | 1.5" plumbing, 17psi normal | TF-100 Test Kit | Liquidator

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    JasonLion's Avatar
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    Re: Black Algae - can/should i use polyquat when shocking?

    Regular shock level is fine. With CYA around 25, shock level is 12.

    Adding polyquat won't help very much, and probably isn't worth the expense. Using borates will help just a little. Frequent brushing while at shock level helps a lot, as does rubbing with trichlor tablets.
    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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    frustratedpoolmom's Avatar
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    Re: Black Algae - can/should i use polyquat when shocking?

    With black algae, all you really need is chlorine and elbow grease. The pq 60 won't really help you here.
    The trick with the BA is to brush it daily to kill the roots - the outer shell is resistant to chlorine so by brushing it you allow the chlorine to attack the insides.

    Normal shock level, 12 is fine.
    Jason and I are typing at the same time
    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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    Re: Black Algae - can/should i use polyquat when shocking?

    It smeared green? usually when I brush off black algae the round disc of black algae gets ripped off leaving a small ring where the algae was at. I don't usually see any green though.
    -Kevin
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    busbeepbeep's Avatar
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    Re: Black Algae - can/should i use polyquat when shocking?

    Mostly it just flaked off, some times it looked a bit dark green.

    Thanks for the advice. Thats what I did last night, I left the PQ out and shocked to 12-13. Added bleach twice to get back to 12. Not sure what the overnight loss was though, didn't get a chance to check until 1pm. With black algae taking a long time to get rid of, will I ever get an overnight loss of 1 or will I have to shock for a long duration?
    17,000 gallon in-ground plaster (circa 1985) | Tagelus 60 Sand Filter | Whisperflo WFE-3 3/4 hp (1.25HP/1.67SF) | 1.5" plumbing, 17psi normal | TF-100 Test Kit | Liquidator

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    frustratedpoolmom's Avatar
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    Re: Black Algae - can/should i use polyquat when shocking?

    It's more about the brushing than the chlorine level - you may not even get an overnight loss greater than 1 (more than likely you will tho). I'd start out by shocking for a day or two and then just keep your FC higher than normal, make your "target" your "min" - does that make sense? and then just brush brush brush. That way you can keep using the pool...brush brush brush!
    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
    http://www.PerfectlyClearPoolService.com

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    Re: Black Algae - can/should i use polyquat when shocking?

    Black algae smeared on a white surface will be dark green. It's algae and has green chlorophyll though isn't visible until thinned out by smearing.
    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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