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Thread: Getting bits of algae growth on bottom

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    Getting bits of algae growth on bottom

    We're entering our sixth year of pool ownership, and I really think I'm learning something new each year. However, I still have quite a hard time with algae and was wondering what I was doing wrong. Right now our pool is clear blue, but there is some slight algae growth on the cove (the part that connects the walls to the floor). I'll try to give as many stats as I can:

    Free Chlorine: 5 ppm or more? (Test kit only goes this high)
    Total Chlorine: 5 ppm or more? (Test kit only goes this high)
    pH: 6.8 (Yes, I know that is too low)
    Total Alkalinity 50 (Yes, this is also too low)
    Cyanuric acid (CYA or stabilizer): 30

    Pool size is 20K. We have a vinyl liner, and it's about 4.5 feet deep all the way across. We are currently using chlorine 3" pucks (using a in-line chlorinator) and dry shock (sodium dichlor). We have a 3/4 horse pump and cartridge filter (75 sq. ft.) I have been told our filter is too small for our pool (the builder who did the pools in our neighborhood back in the 80s used smaller filters to cut costs).

    To give you an idea of outdoor conditions, I am in the Midwest, where we have been getting 80-ish degree weather and high humidity. We also have had some showers come through the area in recent weeks. In addition, the pool is situated on the south side of the house with NO shade, and a white vinyl fence surrounding the pool. Pool temp has been 80 degrees this week.

    It seems every year I always have some kind of algae growth. I usually never have a large bloom where the whole pool is green, but it always seems there is some kind of new growth on the cove or bottom of the pool. Is this normal for my conditions? I always try to keep the chlorine levels quite high, but I'm not always the best on vaccuming or brushing. I try to get to that at least once a week.

    I'm also having a small problem trying to keep the PH and Alk levels up, too. I have been adding baking soda (I think this is used to raise both PH and Alk?) but it seems as soon as it goes up, it's back down again.

    I hope I have given enough information here! Thanks for any suggestions.
    Jennifer

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    JasonLion's Avatar
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    Are you sure of your CYA level? How recently did you test it? Pucks will tend to constantly lower the PH and raise the CYA level. When the CYA level gets high enough you will get algae unless you raise your FC levels also. If your CYA level is really 30 I wouldn't normally expect the symptoms you describe.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Getting bits of algae growth on bottom

    Hi, Jennifer,

    Your low pH is almost surely being caused by the pucks.....they are very acidic (4.7 or something) and will drive your pool pH down sooner than you would think.

    While your Cl is fine now, my bet is it has been quite low in the past, allowing the algae to get a foothold. Your current Cl levels are probably not quite high enough to kick the algae in the butt and get it out of there. I'll also bet that if you could test for CC's, you would be in excess of .5ppm suggesting the need to shock.

    I would download bleachcalc, put in enough bleach to raise your Cl level to 20ppm and keep it there....checking at least twice daily to make sure your back up to 20ppm. Probably in a day or just a little more (you'll know when you can hold your Cl level overnight), you will have shocked the algae out of your pool and you can let the Cl drift back down into a 2-4ppm range.

    Once you get rid of the algae you can address a couple of other issues on your water balance but focus on the algae first.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Thanks for the responses. About two weeks ago, I had the CYA tested at the pool shop since I don't have my own method of testing for it. At the time it was 30. I posted that, because it was the last known result I had available. I will go tomorrow and have it tested again.

    As for the Cl, yes, I did have it drop one time about 2-3 weeks ago, and I am guessing, too, that is where the algae started to show up. My other problem with testing for Cholrine is that my kit only goes up to 5ppm (I have a Taylor kit from Leslies). Does the TFP kit give higher readings than that? I'm thinking about getting one of those -- also so I can test CYA on my own, too. I'd try to kick up the Cl level to 20, but I don't even know where to go for testing to see that it is that high. Leslies uses the same basic kit I do for Cl/PH/Alk, so theirs only goes to 5 as well.

    Also, should I not be using pucks if they are so acidic? I'd like to convert to bleach totally, but I'm still reading and learning on this one. I've been adding 2 lbs. of the dichlor shock on Sunday nights, too.

    Sorry if these are real dummy questions! Chemistry has never been my thing, but I'm giving it my best try. I appreciate the help.

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    Oops ... nevermind, I found the calc! Looks like I'm going to need roughly 5 gallons to get it up to 20ppm. (That's based on having a reading of at least 5ppm right now.)

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    Jennifer,

    You are closer to understanding this than you may think and you're not too far from good pool water

    (Advertisement ) Yes the TFP kit will test Cl about as high as you'd ever need to go....I've done up to 70ppm (boy, was that guy's pool interesting) It will do it dead accurately, too, as well as test for CYA. (end of advertisement)

    Meanwhile, you can dilute your pool water to get a rough idea of high Cl levels:

    1. Do a Cl test with your current tester...say it's 4ppm

    2. Use bleachcalc to see how much bleach you need to get to 20ppm and then add that much to your pool

    3. When you test again, dilute your pool water with distilled water. If you dilute 50-50, you Cl reading in your kit may say 5ppm but it's really 10ppm.

    4. The more you dilute, the less accurate you get, but it should be good enough to get you fairly close....I'd say + or- 4-6ppm

    I think the method above, while a PITA, will be close enough to clear your pool of the remaining algae

    In your case, I'd not use the pucks for a while. Bleach pH is somewhere pretty high (around 10, I think) and will start to lift your pH a little, but not very much. I don't know about the di-chlor as far as pH but bleach will do the same thing and is pretty easy to get.

    Post back with questions it's always rewarding to see someone post back up with CLEAR WATER after a few days.....I think you'll be one of them
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Thanks so much Dave! I just ordered the kit. In the meantime, I'll get my hands on some bleach and try the alternate testing method you gave. Then I can start to tackle the PH and Alk! I'll post again later with some results.

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    Jennifer,
    Could you describe the algae please - color, consistency etc.

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    Jennifer,
    Your CYA is almost certainly much, much higher than 30. That would would be consistent with your long time use of tri-chlor and di-chlor and would mean that you need to keep a higher chlorine level than you probably have been to keep the algae at bay.

    I've heard of pool store testers who take the CYA test result and subtract it from 100. If they did that in your case, that would mean your actual CYA level is 70 but I'll bet it's even higher than that. If you've been on a steady diet of tri-chlor pucks with weekly di-chlor snacks for several years, I think it's safe to assume your CYA is at least 100 (unless you've drained and refilled significant amounts of water in the past year or so).

    If I'm right, your shock level is 25 ppm chlorine. Follow duraleigh's instructions but go to 25 ppm instead of 20. Retest frequently (3 or more times per day is ideal) and add unstabilized chlorine (aka bleach) after each test to return to 25 ppm. Keep this up until the algae is gone AND the pool maintains that level of chlorine overnight. After that, keep your chlorine consistently above 8 ppm and you probably won't ever see algae again. You also probably will rarely, if ever, need to shock again.

    After you've taken care of the algae problem, you should consider draining and refilling your pool to lower your level of CYA so you don't have to keep the chlorine so high. Without an SWG, most people here recommend from 20-50 ppm CYA.

    One caveat to everything I just wrote: Many people, especially and maybe exclusively, those from northern climes who close their pools for the winter, have reported "winter CYA loss" (a highly technical term I just made up) where some or all of their CYA disappears over the winter. The mechanism by which this happens is poorly understood (at least by me). If that happened to you, you could have started this season again from 0 and actually be at 30 ppm. I doubt that scenario though, because you likely wouldn't have algae with 5 ppm chlorine and 30 ppm CYA.

    Best of luck and keep posting questions and results.

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    Thanks Kurt! Good news is that we got a new liner this season (thus new water!), so I only have about 8 weeks of using pucks and dry shock. So the CYA hopefully shouldn't be all that high. (I hope!) Even better news is I ordered a TFP kit last night, so I will be able to accurately test all of this myself very soon! So long Leslies!

    If I followed the bleach calc correctly, I should now be up to at least 20ppm right now. I'll keep on that. Other good news is I have not seen any new algae growth today. The algae is green, and it really isn't all that much in the grand scheme of things. I still have a pretty clear blue pool, but I had been getting small bits of growth on the cove area between the walls and floor. I've been brushing and vaccuming to get the junk out. I'm just trying to stop it all before it becomes something bad!

    I'll stick to just bleach for now. So am I correct in assuming the pucks and dry shock are useless to me now? If this stuff is so bad for CYA levels, why is it even sold? Just wondering if there's anything I can do with it rather than pitching it.

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    Jennifer,

    Don't pitch those pucks just yet. When you go away for awhile, you should be able to use some pucks for proper chlorination while you can't attend to the pool. When you come back, switch from the pucks and your CYA will be little affected.

    Same with the "dry shock" (remember, shock is a verb not a product). You should be able to use it judiciously whenever you need to shock your pool. However, because you're about to get a good grip on your water issues, you may not have to shock the rest of the Summer. Both products have a very long shelf life and you'll find an appropriate use for them sooner or later.

    Why are they sold? Well, we all like the "easy way" and, at first glance, pucks certainly seem like that but they're insidious. They'll eventually get you if you don't use them smartly.

    PS - Your kit shipped today. You should get a tracking number sometime tonight. Thank you.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  12. Back To Top    #12

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    Tiny update: No new algae growth today! I had the chlorine up and brushed the remaining bits last night, and when I came home tonight, I didn't find any new growth! Yay!

    Dave, I also got your message about the kit and FedEx issue. No worries! It will get here when it gets here. I'll have to post some testing results once I get it. I know I'm going to have to work on my PH and Alk next.

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    Jennifer,
    Good news on the algae.

    Please allow me to echo Dave's comments on the pucks, etc. They have their place and will keep for a long time so hold on to them until the opportunity to use them presents itself. By that time you'll fully understand what those products will do to all aspects of your water chemistry.

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