The questions that arise about algae seem continuous, particularly those algae types that are considered a nuisance. New aquarists running a fish only aquarium or a reef aquarium can be subjected to the displeasure of nuisance algae, and the methods of dealing with the problem are all basically the same with small variations.
This question mentions the word ‘red’. Red algae is wonderful, being highly decorous. It is the family Rhodophyta and can be calcareous and all sorts of shapes with varying heights. The high water quality that is more normal nowadays has made the keeping of this type of algae possible.
The picture is spoiled by the word ‘slime’. This descriptive word itself suggests undesirable, and points to [tag-tec]Cyanobacteria[/tag-tec] (name from the microbiology world*), otherwise commonly known as blue green algae. There’s no word ‘red’ there! As I understand it, there is still a dispute among scientists on what this nuisance growth is – in the world of botany* it is known as Cyanophyta – blue green plants. It seems the life form has more in common with bacteria than plants*.
So what has all this got to do with red? Well, despite the name the algae (let’s stick to the name algae, I’m no scientist) can occur as blue green, red and black. Helpful eh! No problem though, whatever the colour appears to be the aquarist will know what it is. It appears as a very thin coating which slowly or quickly spreads. Left alone and without any remedial action being taken, it will spread and cover sand and rocks. Life below will die. So obviously it is not wanted. Another description is smear algae, which describes it well.
So what weapons are at the disposal of the aquarist? Here we go again – high water quality! If any of this algae is spotted the aquarist should check the levels of [tag-self]nitrate[/tag-self] and [tag-self]phosphate[/tag-self] in the seawater. High nutrient levels are normally the major cause. Reduce the nutrients by not overfeeding and carrying out routine water changes. The lack of nutrients will starve the algae, but it will not disappear instantly. The good news is that this smear algae can be siphoned out of the aquarium fairly easily, so this procedure can be carried out at a water change. As time progresses, it could re-appear, so water changing and siphoning could continue for a while (routine water changing should continue of course).
In addition to the above, to prevent re-occurrence the aquarist should check the water circulation for two reasons. First, the algae does not like good water movement (because it is not adhered strongly?) and, second, good water circulation will mean efficient gas exchange. If gas exchange is good, then the seawater will have a high oxygen content and a high redox potential. The algae doesn’t do so well in this clean environment.
So the plan of attack is straightforward.
(*Reference: Helmut Debelius & Hans A. Baensch – Marine Atlas)