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Thread: Black algae...what to do now?

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    Join Date
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    Black algae...what to do now?

    I posted my first thread here quite a few months ago, and I've made some mistakes, and am still learning.

    new-to-pool-maintenance-question-on-de-filter-update-pg-2-t41789.html

    That's the original thread. Since it was so many months ago, I started this new thread. Mods please let me know if you want me to close this one and just continue on from the old one-I know that has been policy in the past, I just figured since it was so long ago a new thread was in order.

    long story short- I'm renting a house with a pool from the 60's/70's that hasn't been maintained at all. The pool guy sucked (1-2 tablets thrown in a week and a quick brush down does not = $130 a month in my book). I came here and threw the chlorine float in the garage and started on BBB, and shocked my pool.

    Here's my original readings from March:
    FC-2.0
    CC-0
    PH-7.5 (it was between 7.4 and 7.6)
    Total Alkalinity-50ppm
    Calcium hardness-480ppm
    CYA- 90ppm.

    I did a small drain/refill, cleaned the DE filter, and got the following readings:


    FC-6.5
    CC-0
    PH 7.5
    TA-60
    CH-450
    CYA-70

    That brought me to mid-april...I figured things were fine and I continued to test weekly instead of daily...then I got lazy...

    I tested weekly for about a month and thought I had it all figured out. I figured I was doomed with high CYA since I wasn't going to empty/refill the pool anytime soon, and figured that I should add about 2-182 oz bottles of bleach every 3 days. Things were going well, or so I thought.

    Some algae started creeping around...some green stuff. I bought a wire brush attachment and would go crazy on the pool for a day and then the next day vacuum all the debris up. I'd do that about once a week. I had to backwash/refill my DE filter once because the PSI changed more than 10 PSI since I cleaned it last (went from 18-30 with all the debris trapped in there).

    Then about a month ago, the rain came...and came and came and came! Here in Houston, it was doing crazy downpours for a good two weeks. I would throw in a bottle, maybe 2 after the first storm or two, but when it rained for a week I got lazy and didn't want to waste money on bleach and shocking it Monday to just have to do it again on Tuesday.

    Now the rain has stopped, and I'm pretty sure it's evident in the pictures in the other thread, but I think I've got black algae...ALL OVER THE POOL. It feels slimy if I haven't brushed in a bit, it scraped with a fingernail black and looks black/green on paper, and it keeps coming back. I haven't shocked the pool in a long time, but it looks like I'm due for some hard core maintenance this week.

    I finally got back out the test kit today and did a full test:


    FC-2.0 (way too low I know!)
    CC-0
    PH 7.8
    TA-80
    CH-380
    CYA-35

    What surprised the heck out of me is the CYA...it went from 70 back in April down to 35 now!? I'm trying to think of why...yes, we had a lot of rain. Question is, where does all the water go when it fills so high? The pool was never overfilling or anything, but the water is going somewhere!

    Second thing is I gotta get that FC back up! 3-7 from what Pool school tells me, and get the PH down to maybe 7.4 so I can combat the algae better? CH seems a bit high, but has always been...I'm not too concerned about that, should I be?

    Really liking this new CYA level if that's true...SO MUCH LESS BLEACH TO BUY! But, I gotta combat the black algae.

    Looking for a plan of attack here...ideas?

    So far I'm thinking:

    1) Shock the pool, brushing every day, for probably a good week (Until the overnight tests is a success and the water is clear). Should I be brushing with the wire brush each time? If so, debris is going to build up on the bottom. Do I need to vacuum this every day or can it sit at the bottom until the weekend, vacuuming once/twice a week?

    2) I'm thinking of using polyquat 60 in conjunction with this. Thoughts?

    I know it's been said before in this forum to just keep going on the old thread, but that was 4 months old...if needs be, please let me know and I'll close this thread and attach this post to my old thread. Lessons have been learned to not get complacent with the testing...that's for sure. I need more regent to test my FC level for my taylor kit as I just ran out today.

    Also, I informed the owners of the problems the pool is having, noting that some pieces of plaster actually chip off, revealing the concrete underneath it. They stated they do not plan on replastering the pool. Short of keeping the filter running, I don't expect anything from them.

    Two pictures of the pool/algae




    EDIT: Just re-tested CYA as I couldn't believe those numbers. My taylor FPD kit (2006 one) goes to 20 on the readings. At around 30 it gets very cloudy and I'm squinting to see the dot, but can barely make it out. At twenty I don't think I can see it. Looks like I might need to boost my CYA up?
    25,000 gallon IG plaster pool
    DE filter Pentair FNSP36
    Centurion 1 HP 1.25SF filter

  2. Back To Top    #2
    frogabog's Avatar
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    Re: Black algae...what to do now?

    Leave the CYA level where it is right now for shocking, it'll take far less bleach. After the pool is clear, then raise CYA.

    I wouldn't decide on the algaecide till after you're done shocking, and have tried faithfully maintaining FC well above minimum. It really should be enough if FC never falls below minimum.

    I don't know about the wire brushing, but definitely brush while shocking. Brush a lot. I'd also be very cautious about letting it fall below shock level at all, so if you've got to be away from the pool and no one can test and re-dose give the pool a nice big tip and add extra chlorine. Guestimate what you might lose, and add that much more. Your pool and equipment is safe up to mustard algae shock level. Use the Pool Calculator if you think CYA is 30, and the Chlorine/CYA chart if you think it's 40ppm to get the highest shock level. Above 40ppm the chart from pool school is more aggressive, under 30 the pool calculator is.

    It's a good idea to give the pool a tip every time you re-dose anyway, that way you can lose a few ppm and still remain above shock level.

    At first, check the water hourly. There will be some big FC losses at first, so make sure you've got a lot of bleach on hand.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  3. Back To Top    #3

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    Re: Black algae...what to do now?

    Could there be a problem Shocking if my cya isn't high enough though? I thought you need at least a bit of cya for the chlorine to bind to, especially with a pool that gets a lot of sun. Just concerned since my second test read possibly 20-30...

    Also I just ordered new regents tonight so once I get them I figure I'll start shocking.
    25,000 gallon IG plaster pool
    DE filter Pentair FNSP36
    Centurion 1 HP 1.25SF filter

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    linen's Avatar
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    Re: Black algae...what to do now?

    30 ppm cya is about perfect for shocking...yes you will loose some to the sun, but you will also not have to shoot for as high an FC.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    UnderWaterVanya's Avatar
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    Re: Black algae...what to do now?

    Lowering ph before you start the shock process could help. Above 10 FC the ph can't be measured accurately. Dropping to 7.2 now will help the shock process as I understand it.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: Black algae...what to do now?

    A wire pool brush is very helpful when trying to eradicate black algae.

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    Re: Black algae...what to do now?

    This will be a lot of work. BA has roots and a protective cap, you have to brush to get the cap off then bring up the chlorine really high.

    I would contact the landlord and suggest that they cover the bill for fixing this. You can offer to do the work if they will pay for the chemicals. Using bleach/pool shock will be cheaper than most pool store chemicals but you will have to keep FC very high for awhile.

    I suggest a very small wire brush, you get more force with it. Not sure if you can attach a small SS brush to a Wall Whale but that is worth looking into.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

  8. Back To Top    #8

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    Re: Black algae...what to do now?

    Quote Originally Posted by anonapersona
    This will be a lot of work. BA has roots and a protective cap, you have to brush to get the cap off then bring up the chlorine really high.

    I would contact the landlord and suggest that they cover the bill for fixing this. You can offer to do the work if they will pay for the chemicals. Using bleach/pool shock will be cheaper than most pool store chemicals but you will have to keep FC very high for awhile.

    I suggest a very small wire brush, you get more force with it. Not sure if you can attach a small SS brush to a Wall Whale but that is worth looking into.
    That'd be nice, but these owners are cheap as heck. The lease contract says I will have it professionally maintained but I already talked to them about that, saying the person they referred me to was doing a horrible job at maintaining it. They really don't seem to care about the pool/property unfortunately. I'm mainly trying to keep the pool decent where I can swim in it for the next 1.5 years until my lease is up and I get the heck out of here.
    25,000 gallon IG plaster pool
    DE filter Pentair FNSP36
    Centurion 1 HP 1.25SF filter

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    UnderWaterVanya's Avatar
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    Re: Black algae...what to do now?

    Quote Originally Posted by nwin
    Quote Originally Posted by anonapersona
    This will be a lot of work. BA has roots and a protective cap, you have to brush to get the cap off then bring up the chlorine really high.

    I would contact the landlord and suggest that they cover the bill for fixing this. You can offer to do the work if they will pay for the chemicals. Using bleach/pool shock will be cheaper than most pool store chemicals but you will have to keep FC very high for awhile.

    I suggest a very small wire brush, you get more force with it. Not sure if you can attach a small SS brush to a Wall Whale but that is worth looking into.
    That'd be nice, but these owners are cheap as heck. The lease contract says I will have it professionally maintained but I already talked to them about that, saying the person they referred me to was doing a horrible job at maintaining it. They really don't seem to care about the pool/property unfortunately. I'm mainly trying to keep the pool decent where I can swim in it for the next 1.5 years until my lease is up and I get the heck out of here.
    Hang in there. With BBB you'll do better than the bad job that service did. There are good pool companies but too many are run and gun - no science to what they do.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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