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  • Results 1 to 5 of 5

    Thread: Question on Algae in an older pond

    1. #1
      koihobo is offline Junior Member
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      Question on Algae in an older pond

      Hi All,

      Long time lurker, first time poster.

      I have been taking care of my disabled parent's backyard pond for several years now. For some background it is about 3000-3500 gallons and 3 feet deep on average. For filtration, my father insisted on trying to go biological only with a bog area when he built it. The bog area is roughly 25% of the square foot area of the pond and feeds into a large-ish waterfall. The pond was not constructed with a bottom drain, and has to be drained and cleaned either yearly or bi-yearly depending on if I got the leaf netting up in time before the first frost and wind storm in the area. I'd like to take it apart and rebuild with a bottom drain but my parents won't allow it. My issue right now is algae.

      In the past I've had issues with string algae growing from the waterfall into the pond. I was able to clear that up this year with the addition of a few more plants and splitting our water lilies; however, a new issue struck as I went from clear water to green water for the first time. I was concerned it was a water quality issue due to lack of filtration or fish load (Currently 4 standard fin and 5 butterfly koi ranging from 4 to 15 in and a few comets). After extensive testing, (daily for several days, then weekly), I only ever had a Nitrate reading of around 20 come back once immediately after a feeding. This may have been a false reading as I tested again a few minutes later with another kit and it came back at 0. It never read above 0 except that one time. Otherwise Nitrite, Nitrate, and Ammonia have all regularly tested at 0 ppm. I tested for phosphates on the recommendation of a local pet store owner who I was buying koi from and that came back at 0 ppm as well. The PH is stable at 8.0 with a KH of around 240 and a GH of 180. Our water in the area is very hard due to living within a few miles of the Great Salt Lake. I've tried oxygenating/submerged plants but the koi just destroy them.

      After trying several water conditioners to try to lower the PH, and having no luck with addressing that or the algae problem. I did more reading and tried putting the pond in full shade. Normally, the pond is in shade from sunrise to about noon, full sun from noon until 6 pm-ish and partial shade until sunset. Within a week of putting the temporary awning over the pond the green water cleared up. I'm now looking for some advice.

      I was planning to build one of the DIY filter projects to try to help with this issue, and incorporate a UV filter into the system. With the shade mostly solving the issue, I'm now wondering if the filter is the way to go or if building a permanent shade structure like a pergola over part of most of the pond would be of better benefit? Maybe both? I also considered expanding the bog area. At this point I'm in a planning stage for Spring and any advice would be appreciated.

    2. #2
      Dovey's Avatar
      Dovey is offline Member
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      I to have extremely hard water and largely natural filtration. The only way I have been able to control the green water algae that literally blows in during the storms to our pool and my pond is to add a UV unit between my pre-filter/pump and the water feature. Cleans it up a treat within a couple of days. But I do also shade my pond during the summer months--for cooler temps, not algae control, however.
      Last edited by Dovey; 4 Weeks Ago at 10:30 PM.

    3. #3
      SimonW is offline Senior Member
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      My experience is that if you increase the pH to above 8 you will kill off the green water algae. Of course, with the side effect of bad water quality due to accumulation of ammonia.

      I guess that your string algae has been removing ammonia-NO2-NO3 from the water, and once you have removed it NH3-NO2-NO3 has been accumulating, which leads to the burst of green water algae.

    4. #4
      koihobo is offline Junior Member
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      SimonW
      I thought of that. The string algae showed up for about 2 weeks after the temperatures warmed up this spring and before the plants greened up. Most of the plants in the pond are a combination of yellow iris, cat-tail species, watercress, and water lilies. Once the watercress came in and the irises and cat-tails put out their new growth the string algae disappeared. My water testing all occurred after the string had disappeared. I've also been testing after putting the shade over the pond to make sure the green water algae wasn't masking a water quality issue and the levels have remained the same. I really and stumped with what caused it unless it was the sunlight and water temperature.

    5. #5
      koihobo is offline Junior Member
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      Thanks Dovey. I'm starting to lean towards trying just the UV unit as far as additional filtration goes.

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