How to Control String Algae in Your Pondless Waterfall

Have you ever seen green gunk clinging to the rocks in your Pondless or Disappearing Waterfall? That’s probably string algae, an organism that commonly hangs out in moist areas, feeding off excess nutrients in the water.

String algae is a natural, normal, expected, and beneficial part of a balanced ecosystem in a pond or waterfall.

Almost every Disappearing or Pondless Waterfall has some string algae. It won’t hurt anything when present in moderate amounts. If you don’t mind the way it looks, you can usually leave it alone.

But what if string algae takes over – or you simply get tired of looking at it?

Fixing the problem is usually easy to do.

At a Glance: 7 Ways to Treat String Algae in a Disappearing (Pondless) Waterfall

Plants pull algae-feeding nitrates out of the water. The more plants you add, and the wider the variety, the fewer problems you’ll have with string algae in the long run.

> Learn More

Unplugging your waterfall for 24 hours lets the sun dry the rocks, killing the string algae.

EcoBlast is a contact algaecide that quickly and safely kills string algae. It’s not a long-term solution – the algae will grow back if you don’t have enough plants to control nitrates – but it works great for persuading stubborn algae to release from the rocks. Find EcoBlast at our Online Store.

> Learn More

Liquid algaecide will also kill string algae. Like with EcoBlast, you’ll still need to make sure your waterfall has enough plants to prevent algae from returning. Find Algaecide at our Online Store.

> Learn More

An IonGen System uses an ion-producing probe to kill string algae without the use of traditional liquid chemicals. Find an IonGen at our Online Store, or contact our Service Team to have us install one for you.

> Learn More

If your Disappearing Waterfall has an Automatic Dosing System installed, use the Prevent for Fountains pouch to help clear up string algae and prevent other issues from cropping up in the future. (This solution only works in spring, summer and fall. Autodosers should be shut down in winter.)

> Learn More

String algae is a normal part of your waterfall’s ecosystem. If it’s not excessive, and it doesn’t bother you, you can leave it be.

String Algae: Is It Normal?

The green stuff growing in your waterfall goes by a lot of names: stringy algae, filamentous algae and fuzzy-type algae, just to name a few. For the sake of simplicity, we’ll refer to all these varieties as string algae, which is basically most kinds of green pond algae you can physically grab a hold of.

String algae is a natural, normalexpected, and beneficial part of a balanced waterfall ecosystem.

How Did String Algae End Up in My Waterfall?

Algae spores blow around in the wind – which is how they end up in your waterfall. They just need moisture and nutrients to grow and thrive.

String algae is totally normal and harmless. These algae live in pretty much every pond and waterfall, where they feed off excess nutrients (nitrates) in the water.

Where do these nitrates come from?  They’re a byproduct of the biofiltration process.  Leaves, pollen and fish waste all contribute to excess nutrients in the water.  This organic material breaks down and creates ammonia. The beneficial bacteria in your biofilter break down the ammonia, producing nitrites. Other bacteria then eat the nitrities, creating string algae’s favorite snack: nitrates.

What happens next to these nitrates? Basically, your plants absorb them and use them as nutrients to grow: to produce beautiful red leaves, beautiful pink flowers, a narrow leaf, a wide leaf. Each of these characteristics uses a different kind of nitrate.

Any nitrates left over after the plants do their snacking will go on to feed stringy,  scummy-type algae in the waterfall. That’s why string algae tends to show up in-force in springtime, when plants are still waking up from dormancy, but it can rear its fuzzy green head pretty much any time of year in any kind of water feature.

Is String Algae Bad for My Waterfall?

Seeing these types of algae in a Disappearing or Pondless Waterfall is completely normal, even if the waterfall is full of plants.  Green fuzziness on the rocks is actually a sign of a happy, healthy waterfall ecosystem.

Stringy, fuzzy algae does all kinds of things to help keep balance in the waterfall.  One of its primary functions is to work alongside your other waterfall plants to remove nitrates (NO3 ) and phospates (PO3).

7 Ways to Control String Algae in a Disappearing (Pondless) Waterfall

You know now that string algae is normal. But not everyone necessarily wants to look at it while enjoying their waterfall.

We do have some tricks to help you get rid of it.

1. Add More Plants

Water Forget-Me-NotThe easiest way to keep string algae at bay is to add more plants to your waterfall. String algae eat nitrates – a nutrient that naturally comes into the waterfall when beneficial bacteria do their work.

Plants also eat nitrates. Each type of plant you add to your waterfall will take in a different kind of nitrate – i.e. a red leaf will absorb one type, a green leaf another. The more and wider variety of plants you add to your waterfall, the fewer nutrients are left to feed string algae.

Variety is important and comes in many forms: different leaf shapes and colors, different flower colors, early-season grower versus later-season, a tropical plant versus a hardy plant.

Not only does having a variety of plants work to reduce string algae, it really makes your waterfall look awesome too!

> Browse our Marginal Plant Library for Ideas

Regardless of what plants you add, you’ll know they’re doing their jobs if they grow big leaves and flowers – meaning they’re taking in lots of nutrients – and the area downstream from them has minimal string algae.

2. Unplug the Waterfall for 24 Hours

String algae needs consistent moisture to survive. Take away the water, and it will dry up and die.

For best results, unplug the waterfall for 24 hours. This dry period will give the rocks a chance to dry in the sun, killing the string algae.

3. EcoBlast

Plants will always give you the best defense against string algae. But if you already have a huge variety of plants in your waterfall, and you’re still not happy with the results, you can buy a few products to give your waterfall that final polish.

The first product we recommend for getting rid of string algae is a powder contact algaecide like EcoBlast (available at Splash and through our Online Store).

Always follow the instructions on the container of any algaecide, but here’s a quick overview of how to apply EcoBlast in a waterfall:

  • Turn off your waterfall 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.
  • EcoBlast takes 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 circulation system back on.
  • Use a net or your hands to skim out the algae as it breaks away from your rocks. Any dead algae you let decay in your waterfall will act as food for new algae, undoing all the work you’ve just done.
  • Wait a couple days to do a second application if needed.

Contact algaecides and algae-control products often work better in warm weather, so you might have to wait longer to see results in early spring than you would in the summer.

4. Liquid Algaecide

Liquid algaecide will also kill string algae. To apply it to your Disappearing or Pondless waterfall, simply pour the algaecide into your basin (where the water disappears) per the dosage recommended on the bottle.

Like with EcoBlast, you’ll still need to make sure your waterfall has enough plants to prevent algae from returning.

5. IonGen

Some pond owners like to install an ionizer for constant string algae deterrence. These devices – marketed under names like the IonGen – release copper ions into the water through a probe, creating conditions that string algae don’t like. They’re a powerful tool if you don’t mind the up-front cost, plus the cost of replacing the probe every one to three years.

Contact our Service Team if you’d like us to install an IonGen in your waterfall, or pick one up from our Online Store for DIY installation.

6. Autodoser with Prevent

The Automatic Dosing System for Fountains automatically adds specially formulated water treatments to Disappearing Waterfalls, eliminating the guesswork and routine of adding products manually.

If your waterfall already has an Automatic Dosing System, simply run the Prevent for Fountains pouch per the instructions. You can double the dosage temporarily if needed, or switch to the Clean for Fountains pouch until water clears. Each pouch treats up to 500 gallons.

Only run your autodoser when temperatures are above 40 degrees. You’ll need to shut down the autodoser in winter to avoid damage to the system.

If your waterfall does not have an autodoser, they’re easy to install. Contact our Service Team, or find one at our Online Store.

7. Leave It Be

String algae is a normal part of your waterfall’s ecosystem. If it’s not excessive, and it doesn’t bother you, you can leave it be.