Have you ever noticed black algae on the rocks?
This pond needs to be cleaned and it is a good example of black algae on the waterfall rocks.Â
Slimy Black Algae
Some commonalities that I have noticed:
- It’s intensely black and has a shiny appearance.
- I haven’t seen it in ponds; this type of algae only appears on waterfall rocks where the water is moving somewhat slowly and thin. (there is another black algae that is spotty and not nearly as intense)
- It can be removed with pressure washing, though it tends to reappear over time.
- It thrives in well-oxygenated spots, especially on rocks near splashing water.
Fortunately, this algae poses no threat to fish or wildlife. In fact, it helps consume organic matter and other compounds in the water, contributing to overall pond health. Many people even appreciate the distinctive look it adds to their waterfall rocks.
This shows a water feature that has been cleaned and the black algae that returned by the Fall. (Yes, from one direction you see a house with siding, from the other you see a brick house. It is the same feature, just from different angles.)
Solution? Try using a mixture of 1 part pond water and 1 part 3% hydrogen Peroxide. Spray it on the area and let sit for 15 minutes. Then rinse it off.Â
Black algae in the pond and on rocks is a sign that the ecosystem is not balanced.
Kristi's Tips
 In the black algae photos above, you can see that none of these features have aquatic plant life. Water is life. Life that looks good needs plants to keep clean! Read more about aquatic plants.
 Only adding bacteria once in a while when you think about it? Can’t manage to put it in weekly? I get it. Use an automatic bacteria doser to keep the right water treatment going in all the time to keep your feature looking its best!Â
* This blog was NOT written by AI. This was written by me. I am not a professional writer, I am a pond person. Therefore, if you see a typo, please forgive me!
*No koi were harmed in the making of this content.Â