Halimeda which is sometimes referred to as the cactus algae is generally an accepted macro algae for reef aquariums. While this type of slow growing aquatic plant is often sought after for its growth rate, ease of pruning and aesthetic looks it also serves as a nutrient export for the reef aquarium.

A couple of months ago I have noticed some new growth in my reef aquarium that I have not noticed before in the four or five years that I have owned this aquarium.  Keep in mind that I built this mini ecosystem from scratch collecting rocks from the Caribbean to Fiji. I noticed that new plant life was developing, this new plant life which I now know as Halimeda opuntia. At first I was pleasantly surprised that I acquired this sought after reef aquarium macro algae even though I did not deliberately purchase or trade for it, It just showed up.  I usually show most uninvited guests the door as soon as I find out that they have shown up but this wasn’t the case with Halimeda.  Halimeda is a flat leaved marine plant that is build on calcium. It is a good sign for reef aquariums because it is a indicator of proper alkalinity and calcium levels.  I have pruned my Halimeda a couple of times since it has shown up and It has a very firm grip on the live rocks it is growing out of.  This Macro algae will turn white (due to its calcium carbonate skeleton) when it is dying or after it has been pruned.