Mastering String Algae in Five Steps

Published on March 21, 2016

String algae manual removal.

Before you can master string algae, you have to learn to recognize string algae in your pond. String algae is a filamentous (stringy filament) species of plant, and is most often found hanging off the sides of rocks or covering the water’s surface. It can quickly grow in weight and length, so it’s best to keep control of string algae as soon as it is noticed.

String algae often clumps and tangles together to form thick blanket like mats — analyze the mats to tell whether it is made of many individual strings.

If so, you’re dealing with string algae.

Is String Algae Harmful?

Though not particularly harmful to inhabitants of the water, string algae is a nuisance to water quality and pond appearance.

It can, however, be a harmful problem if not solved carefully. Many of the methods that remove string algae have a potentially fatal effect, which is why this article’s instructions need to be followed carefully.

Unfortunately, solving a string algae problem is not a one day process. Like most water management techniques, regaining balance after a string algae issue has a varied timeline depending on severity: as short as one week to as long as three months.

5 Steps for Mastering a String Algae Problem

 1. Extract the String Algae Physically — No matter how you go about this process, this first step is essential to getting the recovery process going. To gain leverage and easily pull the algae out, simply wrap the end of the algae around your hand or fingers and pull the algae from it’s root. If the algae is at any sort of depth or extreme in length, you may need to use an elongated tool such as a pole or broomstick to wrap the algae around.

2. Identify the Cause of String Algae — The most common causes of string algae are high pH and Phosphorous (P) levels. The best way to identify what problem you are dealing with is by testing your water quality, once recognized, then you can adjust your pond chemistry based on the following measures.

Lowering Your pH Levels

  • Clear algae blooms outside of your string algae problem
  • Remove or trip overgrown plants
  • Transfer fish to a new pond
  • Experiment with removing rocks that may be contributing (often calcium, limestone)

Lowering Your Phosphorous Levels

  • Make sure no fertilizers are entering your pond (can be water run-off or direct)
  • Remove any algae blooms
  • Scoop out any grass clippings that may have fallen into your pond
  • Grow an Anacharis plant if the problem persists, theis plant feeds on Phosphorus

Although adjusting the pH and Phosphorous levels will set the environment for less algae growth, you must take additional steps to actively work against the algae. This is the key to mastering your algae problem.

String algae blanket.

3. Treat Water and Kill Off Remaining Algae — There are two basic ways to treat the area after a string algae infection: chemical alteration/algaecide or natural bacteria/enzymes. Neither major category is superior by nature, although the natural method is often far safer.

Examples of Chemical Methods

  • Dose Hydrogen Peroxide (3% peroxide, approx. 16oz per 1,000 gallons)
  • Pond Algaecides (Use varies by product, choose carefully and no copper based additives)

Examples of Natural Methods (Can Be Used In Combination)

  • Provide shade coverage over the treatment area
  • Use bacteria or natural mineral based algae additives
  • Enhance your filtration – trickle tower filtration method is best for this cause

I recommend a combination of natural methods to solve a string algae problem, depending on the intensity of the issue. Chemical methods may provide a faster solution to your issue, but without exact measurement they can lead to harm or even fatal consequences for your fish.

**Important Note: UV Lights WILL NOT work on removing string algae

4. Add Extra Plants and Remove Decay — You’ll want to add plants to your pond to provide extra oxygen and to attract snails that will consume string algae. The key here is to bring in plants that have high potential nutrient consumption.

Water Lettuce, Cattails, and Irises during warmer months will help you fight against algae. The Water Hawthorne is the best plant for colder or winter months

These plants will out-compete the string algae for nutrients, making it nearly impossible for the algae to return. Not to mention, adding a lovely plant to your pond environment can never hurt

Unkept pond with string algae.

5. Feed Fish Less! — Overfeeding fish is one of the most common problems pond owners have, and to their own expense. Not only do overfed fish let off ammonia and other potentially harmful chemicals, but if the fish overeat then they won’t have room for other substances in the pond. That’s right, like algae! A key measure of whether you are overfeeding is whether there is food left in the pond after feeding. Your fish should be hungry enough to finish all the food, and full enough to stay healthy.

Pro tip: adding corbicula clams to your environment will make your life much easier. These claims actively filter 1.5 Liters per hour for nutrients!

Fighting string algae can take a lot of time, but if you’re doing it the right way it won’t take many resources. In many cases, removing this problem actually provides an opportunity for pond owners to spruce up the variety in their pond – adding plants, snails, clams, and other algae-feeding inhabitants will certainly add some life.

Safe pond keeping, and thank you for reading! We hope that you are able to take control of your pond and remove any harmful algae that is bothering you.

>> Read “How to Get Rid of String Algae in Your Pond” for more information on the topic

Toledo Goldfish

9 thoughts on “Mastering String Algae in Five Steps”

  1. I have a koi pond with a nice blanket of string algae. It is short and stays that way. But I have been told it is just string algae that the koi are keeping short. Is this true? I have had string algae once before and it was out of control. It seems to me that it is a different type of algae. But a knowledgeable person told me it is the same stuff???

    1. I realize this is an old post and did submit a question to the troubleshooting link. But nowhere can I find out how to dispose of the string algae after removing it from the pond by hand. I have some in buckets, but threw a lot into flower gardens. I removed the rocks that were covered and the algae dried, but will it com back even after drying once it get wet again?
      Should I NOT put the rocks back in?

    1. Avatar photo
      Lora Lee Gelles

      I don’t see any comments on the site about this article from you John. The other questions that people asked about this article have been answered.

  2. Algae can be used as a fertilizer because it is a living organism. When algae is used as a fertilizer, it quickly begins to break down releasing its abundant nitrogen source. As a result, algae can act as an excellent fertilizer that can be used to help grow crops efficiently

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