3 Steps to Get Rid of Green Water Algae


Green pond water won't hurt your fish. But that doesn't mean you have to live with it.

At Splash, all of our ponds are crystal-clear to the bottom, without the use of harsh algaecides or expensive UV clarifiers. We use the same techniques to keep all of the ponds we build looking beautiful year-round.

So how do we do it? Read on ...

At a Glance: How to Get Rid of Green Pond Water

  • The best way to get rid of green-water algae is to take away its food source: nitrites.
  • Beneficial bacteria eat nitrites before green-water algae has a chance to thrive.
  • A regular regimen of beneficial bacteria will keep your water crystal-clear without the use of algaecides or UV clarifiers.

Step 1: Grow Nitrite-Eating Bacteria

Green Pond Water Algae

First, let's talk a little about the reason your water turns green in the first place: green-water algae.

Green-water algae is a single-cell organism that lives in the water and turns it pea-soup green. Your hand will disappear if you reach into the water, but you can't physically pick up the algae because it's too small. (This is different from string algae, which is the gunk you can physically hold).

Green-water algae survives on nitrites that build up in your pond. These nitrites aren't bad for your pond - in fact, they're a natural byproduct of beneficial bacteria breaking down ammonia that would otherwise hurt your fish. If you want crystal-clear water, however, you'll need to grow another type of bacteria that will eat the excess nitrites before the algae has a chance to thrive.

So how do you grow bacteria? The first step is to add lots of nooks and crannies to your pond ecosystem, something you can easily do by lining the bottom of your pond with gravel and installing a properly sized biofilter. Biofilters hold media like filter mats, lava rock and BioBalls that have lots of spaces where beneficial bacteria can reproduce. The biofilter then circulates this bacteria-rich water throughout your pond.

Bacteria need time to grow, which is why newly built ponds are especially susceptible to green-water algae.

Step 2: Add More Bacteria

Ecosystem Pond Algae Control

The second key to growing beneficial bacteria in an Ecosystem Pond is to constantly add a little bit of extra bacteria on a regular basis. You can do this manually once per week using a pump bottle you buy from Splash, or you can take care of it automatically with autodosers.

Once you have all that good bacteria in your pond, make sure you keep it there. Only clean your biofilter once a year - usually in the early spring, before the pond fully emerges from winter dormancy - so you don't wipe out established bacteria colonies. If you must clean it more often, gently rinse it with water from your pond to make the process as gentle as possible.

Don't confuse your biofilter for your skimmer, which sucks in debris like fish waste and dead leaves so it doesn't decay in your pond. You can clean your skimmer as much as you'd like during the season - most people do it about once per week.

Step 3: Enjoy Your Clear Water

If you stop by the Splash Design Center, you'll see that all our ponds are crystal-clear to the bottom. It's not because of anything magic that we're doing other than putting beneficial bacteria in the ponds.

So let's recap: Green-water algae is caused by excess nitrites. We can either feed these nitrites to the green water and enjoy a green-water pond, or we can feed these nitrites to a beneficial bacteria that's growing in your biofilter. If you take good care of your beneficial bacteria - by having a large-enough biofilter, seldomly cleaning that biofilter and building the bacteria colonies with weekly water treatments - your green water problems will go away.

Still have questions about green water in your pond? Don't hesitate to reach out to us at Splash Supply Co.

A Note About Algae Treatments

You might notice we didn't mention algaecides or UV clarifiers as part of our solution for green-water algae. The simple truth is this: You shouldn't need them.

Algaecide will kill the algae, but can also kill your fish if you don't carefully follow dosing instructions. It also does nothing to treat the root of your algae problems - excess nitrites - dragging you into a cycle of constantly buying more chemicals to keep your water clear.

UV clarifiers and sterilizers, on the other hand, don't pose any risk to your pond life. They generally work by moving your water past a UV light that damages algae cells and stops them from reproducing. UV lights will consequently keep your water clear, but, like algaecides, do nothing to treat the cause of green-water algae.

We sell both algaecide and UV clarifiers at Splash for pond owners who want to try them. Be aware, however, that your pond still needs beneficial bacteria to stay clear in the long run.

Learn More About Pond Algae

3 Things to Know About Pond Algae

Pond Ecosystems: How Skimmers, Biological Filters Keep Water Clear

10 Ways to Keep Pond Water Clear

Thinking About Washing Your Pond Rocks? Don't

What Causes Pond Algae?

How Can I Keep Algae Out of My Pond?

Do UV Lights Destroy Algae?

How to Get Rid of String Algae in Your Pond