Have you ever seen green gunk floating at the top of your waterfalls or clinging to your rocks? That's string algae, an organism that commonly hangs out in ponds, feeding off excess nutrients in the water.
Almost every pond has a little bit of string algae in it - and that's OK! But sometimes, the stuff can go crazy and overwhelm your pond. Luckily, if you decide you have more than you want, you can follow a few easy steps to get rid of it.
At a Glance: How to Get Rid of String Algae
- Make sure that what you have is string algae.
- Understand that a little bit of string algae is normal in a healthy pond.
- Add a variety of plants to suck up algae-feeding nutrients.
- Remove existing algae manually or with a contact algaecide.
String Algae: Is It Normal?
The green stuff growing in your pond 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 any kind of algae you can physically grab a hold of. (This differs from green water algae, which turns your water green and requires different treatment.)
String algae can grow just about anywhere in your pond. It can grow on the surface; it can grow down deep. It can grow in a pond that's full-shade; it can grow in a pond that's full-sun.
The first question we get a lot about these stringy, fuzzy-type algae is this: Is it normal? The answer is yes. It's totally normal. We see these types of algae is pretty much every koi and goldfish pond we build.
The reason you see these types of algae in the pond is because of excess nutrients, specifically excess nitrates. Nitrates are a byproduct of the biofiltration process. In the biofilters, beneficial bacteria and enzymes colonize, and they get rid of the ammonia, which keeps your fish happy. The byproduct of that process is nitrites. There's another type of beneficial bacteria that eats the nitrites, producing nitrates.
So the quick science lesson is ammonia gets converted into nitrites, and nitrites get converted into nitrates. Well, what happens to those nitrates in your pond? Basically, your plants absorb them and use those excess nitrates as nutrients to grow: to produce beautiful red leaves, beautiful pink flowers, a narrow leaf, a wide leaf. All of these different characteristics use a different kind of nitrate.
If there's any nitrates left over, then you're going to get stringy, fuzzy, scummy-type algae in the pond. It's totally normal to these type of algae in a pond, even if the pond is full of plants.
Treating String Algae with Plants
You know now that string algae is normal. But what if it's too much algae? Our first suggestion is to add more plants.
Let's say you have a green-leaf plant in the pond and you have a lot of it, but you don't have any red leaves in the pond. Add some plants that have red leaves. The red leaves will take out a red-leaf nutrient, and if the plants take out enough nutrients, the stringy, fuzzy-type algae will be greatly reduced.
Having a wide variety of plants in the pond will greatly reduce string algae while at the same time making the pond look beautiful. So add as many plants as you can to the pond.
Floating plants like water lettuce and water hyacinths have a special talent for taking up excess nutrients thanks to their long roots, which hang down in the water and suck up all of the nitrates floating past them. 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.
Other String Algae Treatments
After you've added all the plants you want to add, occasionally you still have a little bit of excess algae in the pond. In that case, there are some powder-type products on the market today that you can add that act as a contact algaecide.
Keep in mind, though, that if we add algaecide first without adding plants, we're making the problem worse. Dead algae becomes nutrients for next week's algae, so you just end up buying more and more product without actually fixing the root of the issue. You can also remove string algae by hand, thereby preventing the issue of feeding new algae, but manual removal also does nothing to cut back the amount of nitrates in the pond.
At the end of the day, the best way we can recommend to get rid of excess algae is to add beautiful plants to the pond that will get rid of the nutrients. If we get rid of the nutrients, we reduce the amount of stringy, fuzzy-type algae in the pond, and the pond looks beautiful all season long.