Koi Pond Algae – What is it and how to treat it.

outdoor fountains

Does it ever seem like it is algae season? Koi pond algae can be unsightly, but it’s not all bad.

It turns out that there ARE algae seasons!

Just as there are seasons for certain types of vegetables and flowers, there are seasons for particular types of algae as well. Many people call us when koi pond algae pops up and we want you to know that you are not alone!
Although there are thousands of type of algae we simplify it down to 3 types of algae for treatment in ponds.  

String Algae

This is sort of hairy and long algae. It can be pulled it off by hand and you’ll notice it’s not really slimy and has a fibrous feel. A small rake or flat broom works to remove it and it often really holds on to the rocks. It can grow on water lilies too, making it more difficult to get out.

Believe it or not, while this algae can be unsightly, it is helping to keep your water healthy by consuming nutrients in the water. Even in a healthy pond this will pop up now and then. Just pull it out.

When there is a significant amount of it in a shallow stream, we recommend turning the pump off, removing the string algae and then sprinkling EcoBlast (by AquaScape) on, following the directions on the container and letting it sit for a hour. Two days later make sure to give the pond an extra dose of beneficial bacteria.

koi pond algae
This shows string algae. It may look like there are 2 different types of algae in this picture, but these are the same. One is under the water completely and one is floating.  A UV light has no affect on string algae.  A little algae is okay and it needs to be kept under control.  An Iongen can keep algae under control. Removing the algae, treating it with EcoBlast and then installing an Iongen (follow directions carefully) will keep string algae away.

Suspended or Microbial algae

This type of algae looks a lot like green pea soup. While this won’t hurt the fish, it is not pleasant to look at. This is a sign that the ecosystem of the pond is out of balance. Click on this link to the 5 elements to a Healthy EcoSystem to see what is missing.

Adding new plants and consistently dosing with beneficial bacteria will help get the pond back in order. When it is difficult to add marginal plants or when adding gravel is not an option, try adding a pressure filter with a UV light.

Koi pond algae
This green pea soup algae is “suspended algae” or “microbial algae”.  This tells us the ecosystem is out of balance.  A UV light will clear this up if getting the ecosystem in balance is problematic.  Try putting in an Aquascape pond gummy or the Autodose treatment called “Clear”.

When can koi pond algae show up?

Green Algae (both string algae and suspended algae) can appear at anytime but seem to have certain times when they grow the most. Again, this is because the nutrients are just right for them mid-June. The more plants you have, assuming good circulation and aeration, and consistent bacteria, the less algae you will have.

Koi pond algae
Do you ever get this fuzzy algae on the rocks? This just tells us that there are more nutrients in the water than the plants can keep up with. Brush it off with a stiff brush. Add more bacteria, add more plants.
koi pond algae on lily pad stems
The fuzzy algae will even accumulate on the stems of the lily pads. Not only is it not hurting anything, but it helps keep the water clean. Fish will also snack on it.

Diatom Algae

Diatoms show up as a slimy, filmy algae that covers everything.  This is generally golden/brownish/green in color. This may pop up in the spring and early summer.  This thankfully should die back as the conditions change (warmer water and more sunlight). A pond with this sort of algae may need work on the 5 Elements in a Healthy Pond.

Algae in outdoor water features
This bubbly, slimy algae tells us the ecosystem really needs help!  It may require a full cleanout and balancing of the 5 elements of a healthy ecosystem. Lots of beneficial bacteria will be needed to fight this off. 

It turns out that there ARE algae seasons!

The graph below shows the basic seasons of algae. Diatoms pop up early in the season because the aquatic plants and beneficial bacteria are not active yet. The nutrients in the pond are going to be consumed by something, so diatom algae comes in to do the job.

Algae in outdoor water features

Blue Green Algae – Blue Greens (Cyanobacteria) are on this graph and are typically not found during colder springs.  They do come up when we have very warm springs.  This is not a typical koi pond algae and we have never see this in the koi ponds we visit. It sometimes comes up in very large ponds.

Knowing the Ins & Outs of Beneficial Bacteria

Remember that beneficial bacteria needs to be added in weekly and extra at certain times. Read more about Beneficial Bacteria by clicking HERE. (Really there are things you need to know. If you are storing it improperly or using it incorrectly, it won’t help you at all! )