Even though my favorite macroalgae display tank sports so many colors it appears to be a rainbow of magic, there are actually 3 main groups that all macros are placed in. The varying colors are due to the dominant pigment in each algae, the lighting and distance that alga is placed from the lighting, and how healthy it is at the moment. All algae contain chlorophyll, but the red and brown algae have other pigments that are more dominant, so they appear a different color. The color also changes based on the spectrum and strength of light it sits beneath, and even can look differently based on how low or high you place it in the tank. In the following article, I cover the basics of each group, and tell more about some of the algae that I have personally kept from each category.
The green macros : This category contains over 6,000 different species that can look very different, and even grow at different rates depending on whether the type is unicellular, multicellular or colonial. Chlorophyll is their dominant pigment, giving them the green colors. The most common types in the hobby are Ulva, Caulerpas, and Chaetomorpha. These fast growers are best used in a sump or scrubber situation, because they are excellent for nutrient export, but grow much faster than other types of algae. In a display macro tank, the really fast growers are avoided so they do not grow over other alga, and/or use up all of the nutrients so quickly that none are left for other species. However, there are many species that I have kept with no problems such as Codium, and Neomeris is one of my favorites in a display. Green algae will grow even better with iron supplementing and like a lot of light in most cases. I will talk about this more in the lighting and supplement articles.
The red macros: Red algae can brighten up a macro display tank! All algae contain chlorophyll, but the red and brown categories contain other pigments that are “stronger”, which cause the different coloration. The red species dominant pigment is called phycoerythrin. There are so many different types that it can be very difficult to identify specific species, but most algae in the red category are a welcome sight to a hobbyist collecting macros. I personally have jumped for joy when spotting a sprout of nemastoma growing out of a rock! Most types grow much slower than green algae, with the exception of a few species of Gracilaria and maybe Botrycladia, and reds are sought after for their pretty appearance in a macro display. However, the category itself goes beyond the bright plant-looking species to include coraline and other types that grow differently and have a completely different role in an aquarium. My personal favorite reds include Nemastoma, Rose halymenia and Eukemia.
The brown macros: There are more species of algae in this grouping than the other two and are considered the largest category of macros. Most contain a holdfast or root-like structure that attach the algae to a surface (rock for example). The brown color comes from an extra pigment called fucoxanthin, which is “stronger” than the green chlorophyll that all algae contain. The amount of fucoxanthin within the particular alga species is what determines how dark the brown color appears. The two algae that I personally have kept in aquariums are Blue scroll and Sargassum. When kept in the correct lighting, blue scroll can literally shine and almost glow. Sargassum can become problematic, and should be avoided by new macro collectors.