Algae comes from a ver large and diverse group of eukaryotic organisms.  Algae can range from unicellular genera like Chlorella, diatoms to multicellular forms such as kelp as you see in the ocean. Controlling Algae can be tricky and some algae is resistant to some treatment.  Filamentous Algae is very common in ponds cand can be controlled with proper aeration with assistance from dyes and water treatments. Important things to consider most treatment includes a copper compound.  This can be toxic to some fish such as KOI. Most other game fish tolerate copper treatment just fine when applied properly, in fact, copper is used frequently in the Aquaculture industry as a treatment for some fish conditions.