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Thread: Black dots (algae) on the bottom of the pool

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    Black dots (algae) on the bottom of the pool

    I started to see these black dots on the bottom of my pool. I thought they were the diamond brite stones. After taking my brush to them I realized they were small black dots or pockets (capsules) of algae. I try to keep my FC as low as possible in my pool. I am aware of the CYA / FC charts or ratios.

    Question.
    If I brush the pool, breaking the algae pockets, raise my FC slightly higher, and use PolyQuat 60 at the maintenance dose, can I stop this algae from spreading. I do not want to shock the pool. I have a long awaited week off and it starts on Friday.

    Mind you the black dots are few and far between. Maybe a 100 or so. Besides the few black dots the water clarity is 100%

    Thanks in advance.
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    Guest

    Re: Black dots (algae) on the bottom of the pool

    Black algae only takes hold after a long period of too low a chlorine level for the CYA. It does not happen in a week or two. Please post a set of test results. Bad news is it's very hard to get rid of and takes an extended period of high chlorine and a LOT of brushing to kill it.
    Keeping your FC as low as possible has turned out to be a bad idea for you. Polyquat will not kill black algae but it will help. Elevated chlorine levels for an extended period until it is gone combined with brushing will.
    Black algae can damage your plaster surface and often will lead to needing an acid wash if not treated promptly.
    Sorry for the bad news but that's the story.

    These threads on SWG water balance might be useful to you. The first mentions black algae
    viewtopic.php?f=21&t=3663
    category/pool-school/water_balance_saltwater_generator

  3. Back To Top    #3

    Re: Black dots (algae) on the bottom of the pool

    I can't argue with your reply. I have had my FC levels at the bare minimum for quite some time. Those black spots seem to find their way into the small surface defects or they might even be creating the defects.
    I will post my water results on Friday.
    Thanks
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    meatloaf's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    I also have some black dots and a couple of streaks about 11/2" long. I can remove them with a pumice stone only to have them return in a few days. Is this also a form of algae? I only had a few last year but this year I have about 40 spots.
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    My pool is a 10,500 gallon (420 Sq Ft ) kidney shape. A hand made sheer decent waterfeature. STA-RITE HRPB30, Sand filter 30" 98 GPM,
    1 HP Maxi-Glas 2 pump, BBB Method, Taylor K-2005 test kit, 50 Watt 12V low-voltage pond light illuminates the pool at night for a nice soft glow.
    250 gallon stand-alone hot tub. Got it FREE!

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    Firefly2000's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by whowouldfigga
    ....I try to keep my FC as low as possible in my pool.....
    May I ask why you do this? Something to do with the type of surface on your pool or something like that?
    Daniel

    47000L (12500 gal)
    IG Quartzon Interior
    Rolachem Acid & Chlorine dosing
    Paramount In-floor cleaner
    1.5HP pump + Sand filter
    Solar heating under the great Aussie sun!

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    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by Firefly2000
    Quote Originally Posted by whowouldfigga
    ....I try to keep my FC as low as possible in my pool.....
    May I ask why you do this? Something to do with the type of surface on your pool or something like that?
    I just don't like the feeling of chlorine water or dry skin. My other fault is I always want to push the envelope. Keeping the FC chlorine as low as possible ,taking the cya charts into account, was like a challenge.
    It worked fine for almost a year now but we had lots of rain for the last two months and my cya levels kept droping from all the wash out. While at the same time the sun beat down on the pool and my FC kept burning off. I got lazy and stopped using the taylor-2006 for testing the FC and used the taylor k1004 dpd tester. I should of known better than to trust my color blind eye. Keeping the FC low leaves you no margin for error.
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    Guest

    Re: Black dots (algae) on the bottom of the pool

    With a salt water chlorine generator in S. Fl you should have kept your CYA at 70-80ppm and your FC at 4 ppm. If you don't have a metal algae brush then I would get one. You are going to need it to brush the black algae spots. If your CYA is at the recommeneded levels then use bleach or liquid chlorine to get your FC up to around 40 ppm and hold it there while you brush the spots several times a day. It might take a week or two to kill it off. A lot depends on how often you brush and how good you are at keeping the FC up high. The sooner you start killing the the faster you will have your pool back with less chance of surface damage.

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    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by waterbear
    With a salt water chlorine generator in S. Fl you should have kept your CYA at 70-80ppm and your FC at 4 ppm. If you don't have a metal algae brush then I would get one. You are going to need it to brush the black algae spots. If your CYA is at the recommeneded levels then use bleach or liquid chlorine to get your FC up to around 40 ppm and hold it there while you brush the spots several times a day. It might take a week or two to kill it off. A lot depends on how often you brush and how good you are at keeping the FC up high. The sooner you start killing the the faster you will have your pool back with less chance of surface damage.
    Well I used my taylor 2006 test kit today and here are my numbers. The cya caught me by surprise.

    FC 4.0
    CC 0.0
    TA 70
    CYA 40 double checked with a dreaded strip and it does read 40 or lower. Will confirm with pool store.
    PH 7.7
    CH 320
    salt 3100

    My pool brush is made of plastic and stainless steel bristles. Will this suffice for a metal algae brush?

    Raise my FC to 40 WOW!! According to the pool calculator I would need 8gal 3 qts of 6% bleach or 5gal 1qt of 10% liquid chlorine. How many more gallons would I need per day to maintain that level for a week?

    Do I need to adjust the cya now or leave that for later. I figure the lower cya would be good at this point if only to make the chlorine more effective.

    When adding that much chlorine at once I figure my ph will raise considerably. Can I rely on the taylor test kit for a true ph reading?
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    Guest

    Re: Black dots (algae) on the bottom of the pool

    You want an all metal algae brush, they are not expensive. The combo brush is not really going to do it because black algae has a gelatinous cell covering and you need to scrape that off so the chlorine can get to kill it. The reason I said 40 ppm is that high a level combined with a lot of brushing will take care of the balck algae in a short period of time, perhaps a week. You might as well add the CYA now. It's one of the contributing factors to why you got the algae in the first place. Once you kill it maintain your FC a bit higher than normal (say about 6 ppm) for about a month to make sure it does not return then let it drop to about 4 ppm and KEEP IT THERE!

    Don't even worry about the pH until your FC is back at normal levels (or at least below about 10 ppm).

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    Re: Black dots (algae) on the bottom of the pool

    Ok I just got my metal algae brush. 5 pds of cya and 10 gals of 10% pool chlorine.

    How fast can I add the pool chlorine to bring it up to 40ppm?
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    JasonLion's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    You should pour the liquid chlorine slowly in front of a return jet (with the pump running). You can go all the way to 40 ppm without taking a break, just pour slowly.
    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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    meatloaf's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    If your CYA is at the recommeneded levels then use bleach or liquid chlorine to get your FC up to around 40 ppm and hold it there while you brush the spots several times a day. It might take a week or two to kill it off. A lot depends on how often you brush and how good you
    How do you know if you have your FC @ 40? My test kit only gives a max reading of 5?
    My pool is a 10,500 gallon (420 Sq Ft ) kidney shape. A hand made sheer decent waterfeature. STA-RITE HRPB30, Sand filter 30" 98 GPM,
    1 HP Maxi-Glas 2 pump, BBB Method, Taylor K-2005 test kit, 50 Watt 12V low-voltage pond light illuminates the pool at night for a nice soft glow.
    250 gallon stand-alone hot tub. Got it FREE!

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    JasonLion's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    To measure FC levels around 40 you really need a FAS-DPD chlorine test. It is possible to get a vague idea of the FC level with other tests using dilution, but with FC that high the error from dilution is going to be huge, +-16 or so.
    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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    Guest

    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by meatloaf
    How do you know if you have your FC @ 40? My test kit only gives a max reading of 5?
    Then you have the wrong test kit. This is why we recommend either the TF100 or a Taylor K-2006.

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    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by JasonLion
    To measure FC levels around 40 you really need a FAS-DPD chlorine test. It is possible to get a vague idea of the FC level with other tests using dilution, but with FC that high the error from dilution is going to be huge, +-16 or so.
    I was reading my taylor 2006 pamphlet and includes instructions for dilution with high chlorine levels. Should I dilute? From the above post it sounds like I shouldn't.

    If I do not dilute I would use the 10ml water sample level at 0.5 per drop reading.
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    JasonLion's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    The Taylor K-2006 includes the FAS-DPD chlorine test. It is capable of reading very high FC levels directly, without dilution, but it can get tedious (FC of 40 requires 80 drops). When FC is very high and lower precision is acceptable it is often handy to use dilution even with a FAS-DPD chlorine test.
    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: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by JasonLion
    The Taylor K-2006 includes the FAS-DPD chlorine test. It is capable of reading very high FC levels directly, without dilution, but it can get tedious (FC of 40 requires 80 drops). When FC is very high and lower precision is acceptable it is often handy to use dilution even with a FAS-DPD chlorine test.
    I think I will just buy more reagent if necessary and do it right.

    Thanks guys. I brushed the pool and added my chlorine. The pool turned very green. Will keep the pump running for 24 hours a day. I guess I can turn off my SWG. Will try to check my FC Monday am or pm after work. Thanks for all your help. Will keep you posted.
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

  18. Back To Top    #18
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    Re: Black dots (algae) on the bottom of the pool

    The pool water chemistry phamphlet that comes in the K-2006 was written for the K-2005. Taylor never changed anything in it when they included it in the K-2006. Do not dilute when using the FAS-DPD test.

  19. Back To Top    #19

    Re: Black dots (algae) on the bottom of the pool

    Good morning.

    Tested the water at 6.00am FC level went down to 27.5 from 40 WOW!
    Brushed the pool added chlorine.

    I will not dilute with the FAS-dpd taylor 2006 test kit. Need to find more reagent.
    15k Diamond Brite, Aquarite SWG, 1.5hp StaRite, Hayward Star Clear 17502, AquaCal heat pump, Pentair Great White pool cleaner

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    frustratedpoolmom's Avatar
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    Re: Black dots (algae) on the bottom of the pool

    Quote Originally Posted by whowouldfigga
    Good morning.

    Tested the water at 6.00am FC level went down to 27.5 WOW!
    Brushed the pool added chlorine.
    Down from what?
    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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