Fortunately for pond owners, black algae is not commonly found in ponds and watergardens.
Pool enthusiasts however may have to deal with the problem quite
regularly and when they do, they often find black algae difficult to
treat and get rid of.
One of the traits of this algae is that it forms in layers, and
when treated with algaecides or chlorine, the outer layer may be
affected but the remaining "internal" layers remain alive and well.
In some cases black algae will grow in cavities and grout areas
that are recessed, which can make some control even more difficult.
If your pool or even your pond has a black algae problem, ultrasonic algae control
may be helpful. Studies have shown that this technology has been
effective in a variety of conditions, as long as numerous recessed areas
are not present. In other words if the algae can't hide form the sound
waves, it can be controlled.
Other options include intense doses of algaecides and/or chlorine
applications, both of which are primarily advise for pools, or ponds
with no fish present.