Here’s a quick rundown of some of the most widespread
Quats plus copper
Some manufacturers offer useful options for treating black algae,
such as combinations of quaternary ammonium compounds —
“quats” — with metals such as copper, which
disrupt enzymatic activity within the algae cells.
“The quat acts as a wetting agent or a penetrant, and
it’ll actually help draw that algaecidal activity into the
porosity of the plaster, so the copper algaecide actually gets to
those deep-set cells better,” says John Puetz, director of
technology at Advantis Technologies in Alpharetta, Ga.
Just as polymeric quats, or “polyquats,” offer many of
the advantages of quats without a tendency to foam, blended
polyquats include additional ions — electrically charged
atoms — that attract and hold the negatively charged cell
membranes of dead algae cells. These compounds not only kill algae,
they also help streamline the whole cleanup process.
Many manufacturers offer phosphate removers, which help clear out
the phosphates on which algae feeds. However, some recent products
combine phosphate removers with other types of algaecides, such as
quats or metals — thus minimizing available nutrients for
algae while simultaneously killing any cells that remain.