Skip to content

3 Ways to Deal with Spring String Algae

    “More plants, more varieties of plants, more colors of plants…”

    If you’ve been a fan of Splash for any amount of time, you know we love environmentally friendly, fish-safe solutions to most pond problems.  Then, of course, you know we are going to prefer a natural solution when it comes to that stringy, fuzzy, filamentous algae we all get from time to time in ponds and waterfalls.  In this case, that natural solution is PLANTS!

    Those beautiful aquatic plants in your stream and pond compete with the stringy algae for the same nutrients. So when you have lots of plants, you can expect significantly less string algae than you would have without them.

    Our automatic dosing systems do a great job managing and balancing the nutrient loads during the growing season.  But what do you do in late winter and early spring when your dosing system is shut off and the plants aren’t blooming for the season yet?

    At a Glance: How to Get Rid of Spring String Algae

    • Wait for your plants to come out of winter dormancy, and they’ll do most of the work for you.
    • Manually remove the string algae.
    • Try a contact algae-control product like SAB or EcoBlast.
    • Use caution with electronic algae control or liquid algaecide.

    ►►► Remember: It’s completely normal to have some string algae in your pond. It’s part of a healthy ecosystem!

    Why Does String Algae Show Up in Spring?

    During the later spring and summer, plants do a great job of keeping string algae at bay in an Ecosystem Pond. That’s because irises, waterlilies, water hyacinths and other plants naturally remove excess nutrients. Each type of plant eats a different type of nutrient; a blue flower takes up a different kind than a red flower, a wide leaf uses a different kind than a thin leaf, etc.

    The fewer nutrients left in your pond, the less food string algae has to eat – thus our recommendation to add more plants to your pond if you have string algae problems.

    (Note that we’re only talking about string algae here. This is filamentous algae you can pick up with your hand. If your water is green instead of clear, you have a different type of algae that requires different treatment. Click here if you’re not sure which type of algae you have.)

    You’ll probably always see some amount of string algae in your pond, especially before your plants wake up for the season – and that’s OK!

    String algae is a natural, normal, expected and beneficial part of a balanced Ecosystem Pond. It’s totally normal – and actually a sign of a happy, healthy pond when you see green fuzz on the rocks or liner.

    Stringy, fuzzy algae has all kinds of benefits for your pond. One of its primary functions is to work alongside your other pond plants to remove nitrates (NO3) and phosphates (PO3), keeping the ecosystem balanced and your fish friends happy.

    If you can’t stand the sight of the string algae, however, we do have some tricks to help you get rid of it – even in the early spring.

    1. Wait It Out​

    A lot of that bothersome string algae will probably disappear if you give your plants time to do their job.

    As we mentioned above, string algae doesn’t hurt your pond life. If you’re willing to put up with the sight of it for a couple months, there’s no reason to kill it or remove it from the pond.

    Your plants will eventually bloom again. And when they do, they’ll suck out all the nutrients that the string algae is using as food.


    You can continue to control algae throughout the pond season by adding more plants to your pond. While some people especially like floating plants like water hyacinths and water lettuce for the purposes of algae control, really any plant will do the job.

    The trick is to make sure you have lots of plants, and a wide variety. Each one will help clear your pond of the kinds of nitrates that string algae need to survive.

    We also recommend installing an automatic dosing system during the warm months. This system adds a steady drip of beneficial water treatments to the pond throughout the season, helping the plants do their job of keeping the ecosystem balanced and the water clear.

    2. Pull it Out

    Get Rid of String Algae in Pond

    What if you absolutely can’t stand the sight of green gunk on your rocks? Or what if string algae has gone absolutely amok in your pond, distracting from the view of your beautiful fish and waterfalls?

    You have options.

    The easiest and most surefire way to instantly get rid of string algae is to remove it manually. Put on some gloves, grab a bucket and just pull the string algae right out of the pond with your hands or a net.  You’ll find it’s not as slimy as it looks, and you can sometimes roll it up and squeeze out the water.

    This method comes with a few caveats.

    First, make sure you fully remove any loosened algae from the pond. New algae growth will feed on dead algae in your pond if you leave any behind.

    Second, don’t go too crazy scrubbing your rocks. Don’t scrape them completely clean, and, if you must rinse them, try to use water from your pond. Never use cleaning chemicals. Your ecosystem works hard to create colonies of beneficial bacteria that keep your water crystal-clear and your fish happy and healthy, and over-cleaning can wipe out these colonies.

    You have a little more leeway in the early spring before your bacteria have established themselves for the season – that’s why we do pond clean-outs around this time of year – but a gentle approach is always best for your pond.

    Finally, remember that algae will continue to grow back as long as it has nitrates to eat. The only way to remove these nitrates from your pond is to add plants.

    3. Use a Contact Algae-control Product

    We don’t usually like to use algaecides, but certain kinds can help when you have a particularly stubborn algae problem.  For string algae, we recommend using a contact algaecide or algae-control product like EcoBlast or S.A.B. 

    These granular products are easy to use to spot-treat problem areas.  They break down string algae’s cell walls, loosening it from your rocks so you can easily remove it with a net or from your skimmer basket.

    Always carefully follow the instructions on the container of any algae-control product. Generally, though, here’s what you’ll want to do:

    • Turn off your waterfalls if necessary and sprinkle a small amount of the product directly on the string algae. You want to use enough that you can see it on the algae, but not so much that the algae looks like a sugar-dipped strawberry.
    • If you have a lot of string algae, only treat one area at a time. Your fish have grown use to having the algae in the pond and could be overwhelmed if you take it all away at once.
    • Contact algae-control products take effect immediately. The algae will start to bubble and look bleached.
    • Wait at least 10 minutes to give the product time to work before turning your pump back on.
    • Use a net to skim out the algae as it breaks away from your rocks. If you have a skimmer, empty it frequently after application. Any dead algae you let decay in your pond will act as food for new algae, undoing all the work you’ve just done.

    A Note about Liquid Algaecide ...

    It can be very easy to overdose with liquid algaecide.  The active ingredient in most “pond algaecide” is the same chemical that is used in your swimming pool. We frequently see pond owners accidentally adding too much. Liquid algaecide spreads throughout your entire pond, killing algae and removing oxygen from the water.

    You might see the problem here.  Fish need oxygen just like us.  If you use too much liquid algaecide – which can easily happen if you miscalculate the number of gallons of water in your pond – you risk killing your fish and other pond life.

    You still need to exercise caution with granular or powder contact algaecide, but they’re generally safer because you’re only adding them to the parts of your pond where you have a problem.

    What about Electronic Algae Control?

    You may have seen the IonGen™ System on display in our retail showroom.  It is an electronic device for controlling stringy fuzzy algae in ponds, waterfalls, and fountains.  (Please note that it does not affect single-cell green water type algae.) 

    How does the IonGen™ work? 

    As water flows past the copper probes it ‘drips’ an ion into the water. This creates a condition that is unfavorable to the growth of stringy fuzzy algae. It can be effective in some situations where traditional controls like plants and auto-dosing system are not present.

    Stop by our retail showroom or check out all the details on our online store.


    Before installing an IonGen™ System in your backyard koi pond:

    Test the Alkalinity

    The electronic probes may have reduced conductivity or may not function at all in ponds with low alkalinity levels. 

    Required Alkalinity Range: 100 – 250 ppm

    Purchase an Alkalinity Test Kit on our online store:

    After installing an IonGen™ System in your backyard koi pond:

    Test Copper Frequently (IMPORTANT!)

    Regular testing is required to ensure your copper levels do not exceed 0.25 ppm.

    High levels of copper can result in unhappy fish, discolored water and stains on rock and gravel.

    In order for the IonGen System to function properly, you will need to test your water regularly to ensure you are within the parameters below:

    Copper: Less than 0.25 ppm
    Alkalinity: 100 – 250 ppm

    Unplug Your IonGen™ in Winter

    Shut down the IonGen™ System in winter to prevent elevated copper levels. When your plants and ecosystem are dormant, they are not available as a buffer to remove excess minerals.

    A Final Note

    These kinds of products aren’t a panacea for every algae problem. While you’ll probably see short-term results, you’re not doing anything to get rid of the source of the problem: excess nitrates in the pond. You still need to make sure you have plenty of plants in your pond to prevent future string algae growth.

    If you feel like the problem is beyond what you can or want to deal with, don’t hesitate to call us. We’re always available to help you handle any problems that might arise with your pond. Early spring is also a great time to do a full pond clean-out, which helps your pond start the season off right. Just fill out our online form to get started.