Derbesia otherwise know as hair algae is the most common problematic algae that we encounter in the aquariums. The species forms dark to medium colored green strands. Both reef and fish only tanks experience this form of algae and it’s associated (like others) with high nutrient levels.
In no time at all can overtake an aquarium like shown in the above photo. The species will not directly kill corals by stinging of cause tissue recession, however this quick growing algae will acutely just grow over everything. By covering the corals in the tank, they are suffocated from light, and current to neutrally remove their waste product. Typically the corals begin to deteriorate, and die off providing more nutrients for the Derbesia.
As like most prevention of this species is best addressed by controlling the nutrient load in the tank, taking care to match consumption to feeding. Having detritavores in the tank helps. Removal of the Derbesia is fortunately much easier than some of the other algaes. The species is rather tasty to some fish and inverts and therefore is a great candidate for biological control. Effective maintenance is a two part process consisting of Herbivores. The first component is to deploy Tangs to consume to strands of Derbesia. THe fish will typically eat it down to the surface of the rock, but not picking it clean. Secondly deploy snails like the turbo to finish of cleaning the rock.