Coralline algae are divided into two groups:
The articulated (erect), tree like with non-calcified branches attached to the substrate; and the non-articulated (encrusting), the slow growing crusty type on the rocks which this article is focused on.
Coralline algae are plants and need live rock in order to settle and grow. Corallines prefer a moderately lit environment with calcium concentration of about 400 - 440 mg/l, and a carbonate hardness of above 7dkh, preferably between 9-12 dkh.
Kalkwasser is a welcomed source for calcium carbonate and can be added as top-off water. Coralline algae do not respond well to phosphates, nitrates, and elevated CO2 levels. Increased levels will prevent or stun algae growth.
Phosphates should be at 0 ppm and nitrates below 5 ppm.
Best results can be expected at a magnesium concentration of 1400 mg/l Magnesium can be the cause for stunned growth if all the other parameters check out fine.
Coralline algae enter the aquarium in two ways, either they are already attached to the cured live rock, or they have to be seeded. Existing coralline algae can be scraped of the rock or glass of an established reef tank and be collected using a siphon. This sediment should then be applied over cured live rock where it will find hold and start to grow. The more colorful the algae source, the more colorful the newly seeded rock will be.
Coralline algae are considered a vital part in every reef and marine system. The algae produce chemicals that promote herbivorous invertebrates. These in turn keep various sea weeds from growing which would otherwise smother the algae or keep them in the shade.
These “algae” take up carbon for photosynthesis, and calcification where calcium is stored as calcium carbonate within the cell walls. It is also these cell walls that grow across the rock, structuring and holding together the reef set up. Corallines produce a form of magnesium that is beneficial for the invertebrates and the reef environment.
In summary the advantages of coralline algae are that it outgrows the nuisance algae. The healthier the coralline algae growth, the less likely the nuisance algae will grow. Corallines also add lots of color to the aquarium and help to build up a reef tank. It is not the coral that form the reef, it is the coralline algae that cements the particles together thus building the reef.
Last but not least, growing coralline algae is a sign of a healthy environment with good water values. And of course the display of a healthy reef tank is simply stunning.