Blue-green algae
Blue-green algae are not actually algae, but cyanobacteria, which are among the oldest organisms on earth. They do resemble algae and can be recognized by their usually dark blue-green color. They form kind of “sheets” or “oval balls” about the size of a marble and smell bad and they feed on ammonium. So the presence of blue-green algae in the pond indicates an excess of ammonium (a harmful substance) which means that the filter is not working biologically.
It is recommended not to swim in ponds with too much blue-green algae.
Cause of blue-green algae
The number of fish and excessive feeding of the fish can be a cause of blue-green algae. This causes phosphate levels to be too high, 0.5 mg per liter is the maximum. Nitrate levels too low can also be the cause, between 5 and 10 mg per liter is ideal.
Blue-green algae removal
What can you do to remove blue-green algae?
- Remove the dirt from the bottom and clean the filter
- Remove as much blue-green algae as possible
- Optionally, you can administer potassium nitrate to raise nitrate levels
- Don’t overfeed your fish. Make sure the fish eat the scattered food within a few minutes.
