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Controlling Green Water Algae in a Water Garden – Water Garden & Feature Q & A

Picture of Green Water Algae in a Water Garden.


Water Gardens & Features Q & A

Q: I am having a terrible time with green water in my water garden. What can I do? – Abby of California

A: It’s that time of year again when the fish are playing, flowers blooming and your backyard is once again becoming your peaceful retreat, except for that green water in your water garden. Like most of us water garden owners the highlight of our yard is our water feature but what fun are fish if you can’t see and enjoy them? Here are some considerations that may help you take back your water garden.

Filtration: Early in the season your filtration system may not be up to par with the amount of waste and debris left over from the winter months. A good spring clean out may be needed if there is an excessive amount of debris in the bottom of the water garden. If your water garden is relatively clean use a pond vacuum or application of natural bacteria may help get you on your way. This is the time of year to wash out or replace your filter pads to prepare for the coming season.

Fish Load: Have your fish been busy? If your spacious water garden is becoming a full house, it may be time to find a few friends and share the wealth.  Overcrowding is a common source for green water since the filtration system may not be large enough to handle the amount of waste being produced. A simple rule of thumb to ensure room for your fish is 1 fish for every 10 sq. ft. of surface area.

Plant Coverage or Shade: We recommend 40-60% plant coverage in your water garden. This adds to your filtration, since the plants are up taking their nutrients from the water. They also provide the added benefit of shade to help protect your fish from predators. A variety of plants should be used, including: bog(marginal), submerged, water lilies or floating plants. If your not sure what to get, you can check out our aquatic plant packages.

Help Mother Nature Out with Natural Bacteria: Once you’ve checked your filtration, fish load and plant load, it’s time to add some natural bacteria. We recommend the Pond Logic® DefensePAC®. The DefensePAC® is an award winning water garden care system that comprises of 5 products known in the water garden industry as the 5-Steps to Clear Water. They are:

  1. Oxy-Lift™ Defense®: The Pond Cleaner.
  2. Nature’s Defense®: The Pond Balancer.
  3. Clarity Defense®: The Pond Clarifier.
  4. Muck Defense®: The Muck Reducer.
  5. Seasonal Defense®: The Autumn, Winter Prep.

The DefensePAC® is an all-in-one source for water garden maintenance and will keep your water sparking clear all season….guaranteed!

What about a UV filter?: You might be wondering why UV filtration wasn’t mentioned as a solution to green water. Indeed, it is a solution but…it is also can be a band-aid covering up a deeper problem. Always be sure that your filtration is adequate and you don’t have too many fish! You should also be using your test kit to make sure your water is safe for your fish. If everything checks
out ok a UV may be a good tool as long as it is not the only one. Just remember if everything mentioned above is in check the green water should take care of itself and you will have a healthier overall ecosystem.

POND TALK: What kind of green water problems have you had? And what did you do to fix them? Please comment and let me know.

7 Responses

  1. I have 11 small fish in my 11′ x 7′ x 3′ pond. That may be my problem. The green water has gotten worse since I added the last seven fish. I put algae solution in my pond that I purchased on line and it’s suppose to clear up the pond within a few weeks. That was 9/11 and nothing yet. I keep the filter clean and the water fall runs constantly. I have lots of plants that are blooming beautifully but the pond is mostly in the direct sun all day. It’s been a really hot summer in Raleigh, NC.
    I’m getting very frustrated. Help.

    • Laura,

      Couple questions:
      1.) How big are your fish?
      2.) What type of filtration system do you have and what size pump are you using?
      3.) What type of plants are in there? Water Lilies? Water Hyacinth? Marginals?

      11 small fish doesn’t sound too bad depending on how small, small is as well as the filtration you have in there. Just let me know and I will get back to you so we can solve your algae issue!


  2. Jason suggested pressure washing the rocks in my water garden. It worked beautifuly, however, it now appears that the rocks are beginning to build up again with a black/gray coating much like algae. I replaced all the water in my feature after cleaning the bottom.
    I added barley extract, seasonal defense and algaefix but the rock buildup seems to be continuing. Please advise!

    • Doug,

      If I may, I like to ask a few questions. You may have already mentioned this to Jason, but if you could let me know that would be great.

      What is the approximate length, width & depth of your water garden?

      What type of filtration system to you have in their? Is it a Skimmer/Waterfall system, Pressurized Filtration System or something else?

      Approximately how many fish do you have in your water garden?

      Is your water garden located next to trees?

      The reason I ask you these questions, is that build-up are organics that are in your water garden. If we can help limit the amount that gets into your water garden, we may be able to slow if not stop the build up.

  3. I had the same problem with green water the last couple years. I put in a UV system and so far no green water. Now string algae is my problem.

  4. I used every thing there was and the only thing that help my water clear up was a u v clarifier/sterilizer

  5. Two years ago I had a terrible problem with green water. I thought I had tried everything, then I read about Pond Logic Defence Pac. WOW, what a difference in just a few weeks. I also used some barley straw to start but once the pond cleared up I did not replace the straw and the Defence Pac has kept my pond clear. I also purchased a UV light but it has never been out of the box because the Defence Pac worked so well. Thank you for recommending this product, I will never stop using it.

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