Controlling Algae in a Pond

It is frustrating when your beautiful garden pond become a murky green from algae. This is a guide about controlling algae in a pond.

Controlling Algae in a Pond
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I used copper sulfate for algae control in my pond. I ended up killing all my koi. Is there any way to get the copper to dissipate or do I need to drain my pond to reintroduce koi?

Thank you!

    AnswerWas this helpful?Helpful? Yes

    I'd change the water, and flush the pond as well.

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    I have a pond that measures about 30' across and is about 5' deep in the very center, and I want to keep algae from forming without having to treat the water with chemicals, or clutter the pond with plants to block out the sunlight. I have seen ponds that are larger than mine and they have no plants and they are in direct sunlight and the water looks clean.

    Will it help if I have certain types of stones like lime and sandstone in the pond? What would happen if I used salt water rather than regular city water to fill the pond? Please help!



    Hi John,

    First off, I applaud your intention to control algae without chemicals. It is not necessarily the easiest or most convenient fix, but most chemical solutions are only a temporary cure for the problem anyway.

    There are several ways to keep algae under control in your pond without using chemicals. The key is finding which combinations of biological and physical components work best to keep your pond in balance. It may also take some time and patience to figure that out. It is not clear to me from your question whether your pond is stocked with fish, so disregard any of the following strategies that do not apply to your situation.

    1. Assist your plants in keeping your pond clean. Use a vacuum to siphon the bottom of the pond regularly. Remove dead leaves and fallen debris with a skimmer or rake as quickly as possible.

    2. Plant submergible aquatics. They take up nutrients in the water and release oxygen during the day to sustain fish and other aquatic life. They also remove excess nutrients from the water, which discourages algae growth. A rule of thumb is to plant one bunch of submerged plants per 1 square foot of surface area.

    3. Add a barley straw bundle (1 bundle per 1000 gallons of water). As it breaks down, barley releases an enzyme that acts like an organic algaecide. Bundles need sunlight to decompose, so if you try this strategy, don't let the bundles sink to the bottom of the pond. Attach a cork or a plastic soda bottle to the bundle to keep it afloat. After 2-3 weeks, the bale will decompose and provide effective algae for control for up to 3-4 months.

    4. Consider adding a biological filter and beneficial nitrifying bacteria (like Microbe-Lift or Bio-Pond) to your pond. These bacteria feed on the same nutrients as algae and will help keep algae bloom under control.

    5. Algae thrive in full sunlight. Adding enough floating plants (like water lilies, water lettuce and water hyacinth) to cover 1/3 of the surface of your pond will help provide shade.

    6. Use a pump to aerate water and keep it moving-especially near the side of the pond.

    7. Koi eat algae, but they also create waste. Limit fish to one inch of fish for every square foot of water surface in your pond.

    Also, don't be afraid to approach and compliment the successful pond owners you see. They'll probably be more than happy to share their secrets with you.

    Good luck!

    AnswerWas this helpful?Helpful? Yes

    I use an algae control product in my pond that is very natural and easy to apply. It is environmentally friendly, safe on fish, pets, humans and plants. You can even swim in the pond.

    Have them give you a free quote. I'm sure it will not cost much considering it is a very small pond!

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    Is there a recipe for vinegar to use in backyard ponds with fish? The pond has algae on top. I want to kill the algae without killing fish. The algae is taking the oxygen away from the fish. Please help.

    By Shirley from Little Rock, AR

    AnswerWas this helpful?Helpful? Yes

    I use a product called AlgaeFix. It is safe for fish & plants, I have aprroximately 25 fish in my pond & lots of plants & have never had an issues. It works very well.

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    I have a 7000 gallon fish pond with more than 70 Koi fish. I am faced with the problem of algae, and it is spreading very quickly. The walls of the fishpond are marble. One man advised me to put salt into the fish pond to control the algae. Is that true? Algaecide for fish ponds is very difficult to buy, and could not be found. How can I control the algae without damage to the fish?

    By Soe from Yangon, Myanmar

    AnswerWas this helpful?Helpful? Yes

    I have been using an algae control system product that I found to work VERY well. It is safe fish and you can even swim while using the treatment. I would check out this site for more information!

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    How can we balance our goldfish pond water with household products? We are thinking of products like baking soda, vinegar, muriatic acid, etc. We have a 6 foot x 27 foot pond. It is 1.5 feet deep at the shallow area with a 3 foot deep area. We have few water plants and full sun light. There is a homemade 30 gal. sand and gravel filter with a 3 foot to 4 foot long steam. From what we have read we have blooming algae (green water).

    By Billy M. from T Town, AL

    AnswerWas this helpful?Helpful? Yes

    Barley straw and barley straw liquid can be used. It will also go away on its own, If you go online there are many things to buy.

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    My pond holds approx. 2000 lt. It has algae growing on the plants and fish in the pond. How can I safely get rid of the algae?

    By Bruce

    AnswerWas this helpful?Helpful? Yes

    The best and safest to use is Sterile Carp Fish. I ordered mine from a feed store. In no time the algae will be gone. I have used so many products that didn't work at all. My pond is fairly big so I put in 3 of these fish. Oh one more thing, they are really reasonable in price. Hope this helps.

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    What is blanket weed and how do I get rid of it?

    By Romy

    AnswerWas this helpful?Helpful? Yes

    I can answer the first part of your question.

    Blanket weed or silkweed, are very common pond algae and have dense growths of hair-like green strands that float under or on the surface, or cling to plants at the side of the pond.

    I have heard that liquid barley straw extract bought from a garden centre or aquatic nursery, will get rid of it.

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    I moved into a new home and there is a 50 gallon pond in the front yard by front door! It has green algae along the walls. I bought a $50 filter and pump at Lowe's and it doesn't do the job. I have bought stuff to put in the water which also does not seem to help. I went to a pond nursery and ended up buying a PF 300 filter and am going to try to hook it up with the little pump I got at Lowe's. This filter cost me $150.

    The pond is oval and has 2 shelves on either side with a deep center. I feel I am going round in circles to keep clean. Or do I have to! I have no fish as of yet, just one plant, (variegated Japanese iris). Do I need a filter of this magnitude or should I keep pouring in the chemicals (algae killers)?

    By Bonnie P

    AnswerWas this helpful?Helpful? Yes

    Putting some barley straw in a flow through bag will help keep the pond clean. It will not clean the pond, but if you put it in there after you clean it, it will help keep it clean. I"m not talking about using a huge amount, just a small handful in a bag should do the trick. I read about this on the Gardener's supply website.

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    I use Barley hay, you can buy it in bundles of all sorts of shapes and sizes. It floats at first which is great for the frogs to float on. Then it settles to bottom but continues to clean algae. It is said that barley hay was used in the old days for keeping algae controlled in water cisterns and wells.

    By Linda from Troy, PA

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    Is there anything other than bleach or pool chemicals that I can use in my small garden pond to prevent algae? Last year I used laundry bleach and it killed a frog. I have also caught dogs in the pond on hot days. I don't want anything that will be harmful to animals, etc. I've had to drain and clean the pond twice already this season due to the algae and it's too much work to keep doing it repeatedly. There is a water fountain in the pond that runs from 6 a.m. to 9 p.m.

    By Judy from Laurel, MT

    AnswerWas this helpful?Helpful? Yes

    My mother and grandmother used barley straw to keep their ponds sparkling clear/clean. They both had fishponds that were havens for fish, frogs, birds.

    I'm not sure of your budget, but there are plenty of places online to buy it...



    a third-

    and there are a lot more.

    ReplyWas this helpful?Helpful? Yes

    I have a small pond. I would like to know what is best to put at the bottom. At the moment I have a few stones, the water is running clear, but all of the stones are green. Please give me any tips to get them clean. Thanks.

    By Alison from Feltham

    AnswerWas this helpful?Helpful? Yes

    That green you see is algae. It's necessary in your pond, any pond that is in good condition will have it. It's the natural flow of things. It's probably the reason your water is clear. Any flat surface in your pond should be covered with 1-2 inches of small rocks. That prevents dirt/debris from being stirred up from the bottom. If you don't want the green, then you want a swimming pool. If the water is clear that is great. I have never seen any pond or water feature without any green. I say just let it be.

    ReplyWas this helpful?Helpful? Yes

    If I use Shock for a pool and chlorine to reduce the algae, would it be safe to use these items in my water pond if I do not plan on adding fish or plants for a month?

    Hardiness Zone: 6b

    Firsttimepondowner from Wichita, KS


    Reducing Algae in a Pond

    I'm in Zone 8. But when my grandmother's pond covered over with green slimy gunk, we went to the feed store and purchased something that was specific for a pond that would not harm the fish. I can not remember what it was, but the feed store is your best bet, or your county extension agent can help direct you.
    Hope this helps. (06/05/2007)

    By trbrown22

    Reducing Algae in a Pond

    I don't know if it's something you're willing to try, but my dad struggled with algae in our pond for years before finally building himself a bog filter for the water. It's clear as day in there now and all without harmful chemicals. I can't really tell you how he did it, but it was all done in one day once he got the supplies, so it can't be too difficult. (06/06/2007)

    By slippyoink

    Reducing Algae in a Pond

    I don't know if this is within your budget, but it has worked for me. I had so much algae that I couldn't see my fish. Having fish and plants I couldn't use anything that would harm them so I got a UV filter. It was rather expensive, but it has been working like a charm for three years now. (06/06/2007)

    By Connie from Canada

    Reducing Algae in a Pond

    Eek! The residue would definitely be a harm to the plants and fish. That kind of chemical harshness isn't necessary. There are products that you can buy at your local gardening store that won't harm the fish, or try your local pet store.

    The other option would be to empty your pond and scrub it, and then install a fountain to keep the water moving (algae tends to build more when the water is still) or do a waterfall. I would also get some koi or other fish and a scavenger that likes to eat the algae. (06/07/2007)

    By cfbandit

    Reducing Algae in a Pond

    You could try barley straw:

    This isn't harmful to either plants or fish.

    By ThriftyFun

    Reducing Algae in a Pond

    I think if you aerate the water with a small submersible pump made for ponds, and add a couple of carp fish that should take care of the algae. Algae is a source of food for fish, oxygen is needed to keep the water fresh and so if you get the pond back into some kind of balance, the algae will be controlled. (06/07/2007)

    By Hedera

    Reducing Algae in a Pond

    Thanks everyone! I am trying some stuff that is a bacteria, the good kind and is supposed to help. I also have a barley bail, but it was said that this will be more helpful as time goes on. Although my pond is still green, I was told it is safe enough for fish and plants. These two elements plus the bacteria supplemental are supposed to help balance everything out naturally. Apparently my pond looks worse than it is probably due to the rain we had and now it is hot and sunny. The bloom happened rather quickly, and I hope it goes away soon.

    Thanks! (06/07/2007)

    By newpondownerin wichita

    Reducing Algae in a Pond

    I read your question and started to answer then it dawned on me you were talking about a small pond. I have a one acre, 20 foot deep, spring fed pond and controlling green gunk, etc. in it requires shading the water with a blue dye (4 gallons at $50.00 a gallon) and chemicals which do not hurt the fish (bass) or ducks/ turtles. We do aerate the pond with a large pump and it sprays the water up 25 feet into the air and when it comes down like rain it helps break up the green gunk. (That green gunk is generally caused by decomposing vegetation on the bottom of the pond releasing it's gases and too much sunlight). The green slim is just too much sun. They are signs of a healthy pond, but it doesn't look too nice to most folks. (06/10/2007)

    By Jimmy2N

    Reducing Algae in a Pond

    Best thing you can do is barley bails. So natural and the water is absolutely so clear you can easily see to the bottom of a 4 ft depth. It might take a week or two depending on the severity of your "slime", but we tried chemicals and this beats it hands down! (07/11/2007)

    By Lynn

    Reducing Algae in a Pond

    The problem is all the silt that ends up in the bottom of your pond. The answer is to get oxygen down to the bottom of the pond so that the decomposition of all this organic material can begin. This cannot be accomplished with a surface fountain, they only recirculate the surface water and do nothing to get oxygen in the bottom of the pond. The only product for this is a pond aeration windmill. These are decorative and cost efficient. Once they are in place, they cost nothing to operate. Check out a company in Springdale, AR, called Outdoor Water Solutions for your answer. (12/07/2007)

    By Bob

    CommentWas this helpful?Helpful? Yes

    Q: I am desperately looking for a way to stop algae from growing in my small pond with goldfish in it. It is a container pond and I have tried everything. Does anyone have any home remedies?

    Thanks in advance,

    A: Michelle,

    Algae multiply rapidly under the right environmental conditions-especially in water containing excess nutrients (phosphate and nitrate) while having access to a lot of sunlight promoting photosynthesis. Effective control requires depriving algae of food and/or light.

    Here are a few natural ways to control algae:

    Don't overstock your pond with fish. Decomposing organic waste from fish provides a continuous supply of nutrients for algae bloom and string algae. Keep your pond clean by regularly vacuuming the bottom to prevent build up of these nutrients along with frequent partial water changes.

    Shade can be supplied with plants such as water lilies and water hyacinth. However, because the pond's primary source of oxygen is at the water's surface, too many surface covering plants can result in low oxygen levels (signaled by gasping fish). You'll need to provide additional aeration and/or reduce the number of fish in your pond if you want to maintain extensive surface-covering plants.

    Consider shading the pond's surface with a type of canopy made from shade cloth or lattice. Many aquatic gardeners find this inhibits growth of algae while protecting flowering aquatic plants from excessive sunlight and heat. This method will also protect your koi's colors and protect them from overhead predators.

    If all fails, there are a number of algae controlling additives available that are safe for fish and aquatic plants.


    Keeping Algae from Growing in a Pond

    pine straw (07/17/2005)

    By ken.

    Keeping Algae from Growing in a Pond

    Cover at least 60% of the top of your pond with water plants, they will starve out the algae. Also keep pond shaded as sunlight promotes algae growth. (07/18/2005)

    By Anonymous

    Keeping Algae from Growing in a Pond

    Try throwing a handful of new copper pennies in. The copper sulfate discourages algae growth in water. I use them in my aquariums. This is not an "instant" fix, takes a little time for copper to leach out of pennies, but it does work! Happy gardening.
    Joyce (07/18/2005)

    By Joyce

    Keeping Algae from Growing in a Pond

    I have been having the same problem with my small pond (100 gallon). I resorted to taking the pond out and pressure washing it, then when I put it back in and refilled it i started treating it with "ALGAE DESTORYER ADVANCED". A big bottle of it at Walmart sells for $8.93 and it only takes 2 teaspoons every 3 or 4 days to treat a pond the size of mine. So far the water is staying nice and clear and the fish seem healthy (its safe for fish and plants). (07/20/2005)

    By mamaboo

    Keeping Algae from Growing in a Pond

    Find some small pelleted food for your fish. Only give them enough food that they can eat in 5 minutes. I have a small pond and I don't feed the fish every day. I was told that if you have some floating pond plants in your pond the fish will find enough food to live on for several days. Also you might try to find some "water shade" tablets. They turn the water a beautiful shade of dark blue and that helps keep the sunlight out so the algae won't grow so much. I found some water shade at Home Depot in the pond department. Remember some algae growth on the sides of your pond is normal and healthy so don't try to eradicate all of it. Hope this helps. (07/30/2005)

    By Jeri

    CommentWas this helpful?Helpful? Yes
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