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Thread: Yellow algae

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    Yellow algae

    Hi there!

    I have never used the BBC method until just recently due to a bloom of yellow algae. My other half convinced me to "save money" by not maintaining our pool over the winter. Long story short, I was able to bring our swamp back to pretty darn clear water. However, it looks like I have yellow algae blooms on the sides of my pool (slightly more yellow on the sides that are more shaded). When I brush the sides, it looks like a bit of algae brushes off. I noticed the high FC levels required for shocking to kill mustard algae. I ended up draining and refilling the pool due to high CYA levels (100 due to using the chlorine pucks). After the refill, I balanced the water, checked the readings and proceeded to SLAM, my readings were:

    FC: 0
    pH: 7.4
    TA: 90
    CYA: 0
    CH : 120

    I know my CH was on the low side but I figured I could take care of that after I killed the yellow algae.

    I used the pool Calc and saw that I would need to maintain chlorine at levels above 12ppm. I think my mistake was not taking pH readings, but my understanding was that pH readings would be skewed due to high chlorine levels. I have been brushing the pool each time I test at 3 hour intervals during the day starting at 8am until sundown. The FC levels typically drop about 1-2 ppm nightly but is heavily consumed during the day, specifically towards the afternoon, about 2pm - 6pm (6-8 ppm drop within 3 hours). I have been trying to maintain at least 16 ppm because of the drastic drops but it doesn't seem to get rid of the yellow algae. It looks like it gets better when I look at it during the early morning to noon. The yellow appears to fade a bit, but by 3-6p it seems like all the algae I've brushed off seems to magically reappearing. What am I doing wrong? I've been trying to maintain the high FC level for almost a week now with no improvement. Today, I took readings and was astounded to see that the pH level has skyrocketed.

    FC: 30
    pH: 8.0+
    TA: 110
    CYA: less than 30...i used 5 pucks during the whole process
    CH: did not take this reading.. Is it necessary?

    I've gone through pool school and understand the basics. I know my pH levels are high and am looking at bringing them down based on the acid demand test (I own the Taylor K2006 kit.) I am confused as to how did my pH get so high? I vaguely remember reading that high chlorine levels skew pH readings. I am now thinking that I may have whacked my pH out of balance. Also, how long does SLAMing usually take? I am trying to be patient and keep the levels high for a week but my concern is that I don't see progression during the week. If the yellow got lighter day by day, I would have more patience. However, I feel that I'm at square one everyone I go out to look at my pool in the afternoon. Help! So frustrated right now.


    Thanks!


    Playas Del Coco, Costa Rica
    36'X16' in-ground. 25000 gallon
    3/4/HP Hayward with 280 pound sand filter
    AquaRite SWG

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    Richard320's Avatar
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    San Dimas, CA (LA County)
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    Re: Yellow algae

    STOP!!

    Your pH is not that high. Above 10 FC, the pH test reagent reacts with the chlorine and makes it reads falsely high. So don't mess with it! When the FC level drops down, then test and adjust it.

    Proof. The captions somehow got lost during the transition to the new server, but 1 & 2 are exactly the same water sample - same pH - just much higher FC levels. Don't adjust your pH.

    I'm not sure what to tell you about the mustard algae, but don't add any more acid!


    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Yellow algae

    Oh poo... I ran an acid demand test and added almost 2qts of MA. So does that mean I need to bring let the FC level come down to around 3-5ppm and test for pH and start over?

    Playas Del Coco, Costa Rica
    36'X16' in-ground. 25000 gallon
    3/4/HP Hayward with 280 pound sand filter
    AquaRite SWG

  4. Back To Top    #4
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Yellow algae

    Quote Originally Posted by gy View Post
    Oh poo... I ran an acid demand test and added almost 2qts of MA. So does that mean I need to bring let the FC level come down to around 3-5ppm and test for pH and start over?

    Sent from my Nexus 5 using Tapatalk
    I wouldn't bother. You'll be losing ground. Just ignore everything but FC and CC until you pass the three tests and you're finished with the SLAM. The rest of the chemistry can be fixed in an afternoon once the water is clear.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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