FORWARD: This Aquarium Answers article (post) is not intended as a complete algae control article, but is intended to address the types of algae that I receive the most questions about which are Brown Diatom Algae, Freshwater Thread/Hair Algae, Black Beard Brush Algae (BBA), and Marine Hair Algae aka Filamentous marine algae (I address other algae as well in this article).
The bottom line is I do not claim that this article is the "end all" for algae control, but I do think the majority of readers will find this article useful, often with information not found elsewhere.
Updated 7/2/16 Brown Algae is not considered a true algae as per many biologists, rather a diatom.
However under the 5 Kingdom classification system both Brown Diatoms and more common algae fall into the "grab bag" Kingdom; "Proctotista", although Brown Diatom Algae fall into the division Bacillariophyceae.
What is also noteworthy is there is evidence of some diatom "algae" as a green colored slime like algae instead of the much more common brown diatom algae that is a common problem with new aquariums.
This has been called "Green Snot Algae" (scientific name Didymosphenia geminata) and is becoming more common in streams just under the surface and/or covering rocks (pictured to the right).
Also commonly known as didymo, this is a rapidly spreading invasive species of diatom.
References: Wikipedia; Didymosphenia geminata Didymo risk goes beyond green snot in rivers What are Diatoms? They contain two types of chlorophyll and at some stage in their life cycles have motile stages which move by the action of one or two tiny beating hairs called flagella.
Diatoms also single-cell organisms but are significantly larger and more complicated than cyanobacteria. Most diatoms show very limited mobility and exist primarily as groups of cells growing a film over the surface of objects.
In low concentrations they probably don't have any noticeable effect in aquarium systems, and indeed they are probably always present.
These diatom cells are encased within a unique cell wall made of silica (hydrated silicon dioxide).
The yellowish-brown chloroplasts within Brown Diatom algae are what give this “algae” its typical appearance.