Things You'll Need
Chlorine test strips
Mustard or black algae is generally only found on shallow water, garden-type ponds. For deep, or natural ponds, use the steps provided for green algae.
Algae are the greenish brown or black growth on the surface or walls of ponds. They thrive and survive on organic compounds that are present in the water. These organic compounds are most present in sitting water. The multiple types of algae include green, black and mustard. Having an excess amount of algae in a pond can be harmful towards other life in the pond such as fish. Algae can be treated through the use of chlorine.
Add chlorine to your pond water to get the chlorine levels to 30 parts per million. The amount you need to add will depend on your brand of chlorine and the volume of water. Check the label. Test strips available at most pool stores check the chlorine levels of your pond with reasonable accuracy.
Allow the water to sit for 24 to 48 hours.
Vacuum out any dead algae. For natural ponds, skip this step.
Apply an algaecide to your pond to prevent further outbreaks.
Mustard and Black Algae
Use a brush to brush the algae spots.
Add chlorine tablets to each of the spots that you brushed.
Pour algaecide onto the spots.
Allow the spots to sit overnight.
Brush the dead algae again to loosen it.
Vacuum the bottom of the pond to suck up loose algae. If you have a deep pond, or a natural pond, you can skip this step.
Bryan Clark has been a freelance writer since 2002. His work has appeared in "The New York Times," "USA Today" and the U.K.'s biggest paper—"The Guardian," amongst other, smaller publications.