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Controlling Algae in a Pond

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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.


Solutions: Controlling Algae in a Pond

Read and rate the best solutions below by giving them a "thumbs up".

Tip: Clearing Murky Pond Water

Water lily in pond with fish below.There is a growing trend in gardening of adding water features to the yard and garden. Installing a pond to your landscape gives your garden a sense of peace and serenity and makes a delightful addition for backyard wildlife. Neglecting to maintain it, however, can quickly turn your tranquil pond into a smelly, murky headache. Here are some ways to clear up murky pond water.

Too Much Algae

Murky brown water is almost always caused by an excess of algae. Some types of algae float to the top and "bloom," while others remain suspended in the water column, causing the water to look dark. If your pond contains fish, chemical controls may not be safe for them. One safe and economical solution is to submerge barley straw wrapped in netting into the water. As is decays, it releases a chemical that inhibits algae growth. Anchor it to the bottom with a brick or large stone and change it every 6 months.

Too Many Fish

A pond that is overstocked with fish is prime for algae problems-excess waste (nitrogen) stimulates algae growth. Most pond gardeners calculate the number of fish for their ponds according to the surface area or the number of gallons of water it holds. This might work to start with, but it won't be accurate for long. Remember, fish grow! Consult with your fish supplier to find out how large your fish will grow under ideal pond conditions. Don't forget to add snails, bottom feeders and if possible, some freshwater mussels to help gobble up the algae. According to the USDA, non-aerated ponds should have no more than one, 12" fish per 10 square feet of surface area. (To calculate surface area multiply the length x width of your pond). Aerated ponds can have up to one, 12" fish per 2-3 square feet. They also recommend that the average hobbyist stay well below these guidelines.

Too Much Fertilizer

Fertilizer leeching in from the lawn or nearby flower beds can overburden the pond's nitrogen load. Avoid using fertilizers where there is a risk they will contaminate your pond water. Traditional fertilizer mixes will promote algae growth, so use a soil mix designed for potting aquatic plants when adding them to your pond. Even then, try to keep the mix confined to the plants by lining underwater pots with burlap and weighing down topsoil with gravel and rocks.

Too Much Sunshine

A lot of sun may be great for the rest of your garden, but too much sunlight streaming into your pond causes excess algae. Site your pond strategically near buildings and fences which will cast a shadow over your pond for at least part of the day. The addition of surface plants like water lilies will also provide shade and help hold down the water temperature (algae love warm water). Add a variety of underwater oxygenating plants like Elodea, Microphyllum and Ceratophyllum (1 bunch per 8 inches square). They will help keep water oxygen levels high and algae levels low.

Too Much Tap Water

The chemicals that sterilize our tap water can actually work to increase algae blooms. When you refill your pond, try to fill part of it with some water from a stream or even another pond. Nature's water contains insects and other organisms that will help keep the algae population down.

Too Much Plant Debris

It's important to keep your pond free of decaying vegetation. As plant materials decay under water, they release nutrients that stimulate algae growth. When your pond freezes over in the winter, this decay can also cause toxic gases to build up under the ice. Trim dead or dying foliage from plants located around the margins of your pond. If overhead trees are a problem, consider erecting a frame around the pond so you can cover it with a canopy as necessary or clean leaf debris out daily with a large net.

Not Enough Patience

It can take several months for a new pond to reach an ecological state of balance. In the first few weeks-sometimes months, your pond's water may look murky and even when in perfect balance, it won't be 100% clear any more than a pond in nature would be. The worst thing you can do during this time is keep cleaning and refilling your pond in an attempt to achieve clear water. Every time you do this, the pond has to start over trying to reach a state of balance. Be patient! It will be worth the wait!

By Ellen Brown

Tip: Controlling Algae in Ponds

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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Here are questions related to Controlling Algae in a Pond.

Question: Can Salt Control Algae in Fish Pond?

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


Most Recent Answer

By JB07/07/2008

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!

Question: Killing Algae in Backyard Fishpond

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


Most Recent Answer

By Stacey [3]06/06/2010

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.

Question: Keeping Algae from Growing in a Pond


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!

By Ellen Brown

Most Recent Answer

By JB07/07/2008

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!

Question: Controlling Goldfish Pond Algae

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

Most Recent Answer

By HAPPYINHARNED [13]05/29/2012

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.

Question: Killing Algae in Backyard Fishpond

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

Most Recent Answer

By Janette [87]10/25/2013

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.

Question: Controlling Duckweed

Is there anything to control duckweed in a pond?

By Romy

Most Recent Answer

By smith21 [3]06/27/2013

Hi friends...
I have a pond few days ago it was covered by duckweed I used Hydra Dw-400 and it was amazing it really worked. I was totally impressed by this product. So I will suggest you to use this it will really help you.

RE: Controlling Duckweed

Question: Getting Rid of Blanket Weed

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

By Romy

Most Recent Answer

By David M. [1]07/01/2013

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.

Question: Reducing Algae in a Pond

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

Most Recent Answer

By Jarron [7]08/17/2010

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.

Question: Keeping Pond Stones From Turning Green

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

Most Recent Answer

By Janine06/23/2010

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.

Question: Using Muriatic Acid to Clean Fish Pond

Will a weak solution of muriatic acid harm fish in a pond?

By Sandy D

Question: How to Clean Green Ponds?

My pond is heavy green. How do I clean it having 2 filters in it?

By smith21

Question: How to Clean Green Ponds?

My pond is heavy green. How do I clean it having 2 filters in it?

By smith21

Question: Clearing Pond Green Water

How to get rid of pond green water?

By Romy

Question: Keeping Sand in a Fishpond Clean

How do you keep sand in a fish pond clean, so that it doesn't turn green?

By Annette v from Edmonton, Alta

Question: Green Pond Water

I have a 2500 gallon pond with two waterfalls. I have tried beneficial bacteria, SAB, and algaecide to no avail. It is still murky. We have a few plants and only 5 goldfish in the pond. The pond is in the sun part of the day. I am at my wits end. The pond will go from clear to murky in a matter of a day. What am I doing wrong?

By Doris

Question: How Can I Clear Up Murky Green Pond Water?

I have a new pond and have filled it from a neighbor's pond that is to be cleaned out. The water is pretty green and fuzzy looking. He has a woods near by, and was always fighting leaves (black settlement on bottom). He has used a lot of copper sulfate in the past. What would be best way to clear up the water? Any help please!

By Todd from Lima, OH