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Controlling Algae in a Pond Containing Trout – Pond & Lake Q & A


Q: How do you control algae growth in a small pond that will not affect the fish (trout) in it?
-Jerry of Harrisburg, PA

A: We always suggest to customers with a pond of any size to use an aeration system along with natural bacteria to help eliminate muck and prevent stagnant water. Using these products together will make pond management easier and in time will reduce the need for chemicals. As far as the algae you currently have, there are a couple options to get rid of it. They are Algae
Defense Algaecide
and Hydrothol 191 Granular. If you use the Algae Defense, you will need to test your water hardness to ensure the carbonate hardess is above 50 ppm (parts per million) which is safe level for trout when treating with Algae Defense. If you do not wish to go that route or if your pond contains koi or goldfish, use Hydrothol 191 instead. Hydrothol 191 is a granular that will work both on algae and weeds.

Just remember, using only chemicals to control algae is a “reactive”, short-term approach. If you really want to gain control over the long-haul, then you need to be “proactive” and follow the 4-Easy Steps to the Perfect Ecosystem. Watch our 4-step video online to learn more.

4 Responses

  1. Ed Love,

    Having a fish kill even when having an aeration system tells me one of two things: ONE, the trout are dying because of a copper-based algae treatment, or TWO, there is not enough aeration to prevent turnover from happening.

    When treating a pond containing trout with any chemical that is copper-based, the carbonate hardness of the water must exceed 50 ppm or parts per million or the trout will be harmed. Before treating your pond for filamentous algae, get a carbonate hardness test kit and test the water. If the hardness is not above 50 ppm, do NOT treat your pond with a copper-based algaecide or herbicide.

    To test to see if your pond is sufficiently aerated you can do two things. One way is to jump in! If the water temperature at your feet is a lot cooler than the water temperature at your chest, then the pond is not sufficiently aeration. Another way to test is to use a boat and float over to where the diffuser bubbles are coming up from the bottom. If the water temperature around the bubbler is a lot cooler than the water temperature away from it, then the pond again, would not have sufficient aeration.

    Hopefully this hopes. Keep me posted!

  2. pond guy,
    I have a pond that is 80 yards long by 20 yards accross and 12 ft deep on average, then attached, there is also a “loop” of another 70 yards by 10 yards by 10ft deep. I stocked it with 125 4″ brookies and rainbows. I have two wind assisted aerators, and one electric should the wind not blow. I also have a 10 gal/minute circulating pump. I have filament algae problem, and for the second time in six years, once the fish are averaged size of 2-4 pounds, complete fish-o-side occurs –all floating within a week. By the time this happens (usually late august) I have fished 20% of the stock out. I use blue shade for the water and feed with commercial fish food product. Help please do I use algae killer, less fish, or give up?

    Sick of burying fish.

    ed

  3. Matt, I have just a couple questions for you so I can get you the best answer. First, what is the approximate length and width of your pond? Second, what type of algae problem are you having? Is it Chara, a thick, smelly, weed looking algae that grows from the bottom up or is it filamentous algae, the floating mats? Lastly, what kind of fish do you have in your pond? Do you have trout, koi or goldfish?

  4. I always see data about controlling algae etc for people who have ponds with fish or plants. I have a small pond with a stream (recirculating) that runs into it. I am pushing about 60 gallons per minute through a 240V pump. My pond and stream get pretty nasty with algae and eventually i have to drain the water, scrap it and start over. Can you make any suggestions how i could keep the water nice and clear? I don’t mind a few chemicals but i don’t want to kill the birds etc that drink from it. thank you. m.

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