In the past, saying the word “algae” to a saltwater hobbyist would result in a disgusted look and probably a little cursing.  Hobbyists’ thoughts went directly to the algae that covered their glass, rock and/or coral, ruining their beautiful display.  Most articles and discussions about algae dealt with how to get rid of it, and focused on methods to keep a tank algae-free.  Not only is an algae-free tank impossible, algae is actually a sign of a healthy system.  In fact, algae are “primary producers” who provide food and other benefits to the other organisms (like fish) who cannot produce their own foods.  Besides, if algae did not grow in response to the light and nutrients in a system, hobbyists would have a much more difficult time keeping up with maintenance.  There are many different types of algae, and letting them grow out of control can become a problem.  But, algae in itself is never bad.

Luckily, as more people tried different methods to get rid of these nuisance algae, we began to understand why it grows in the first place, and how we can use it to our benefit!  We also realized that there are some types that are extremely pretty, do not grow very fast, and can look as amazing as any coral when taken care of properly.  Oh yeah, and seahorses love them! The role of algae in saltwater tanks has changed so drastically that some hobbyists (myself included) even set up a display tanks with macro algae as the main attraction.  For macro algae to change from something that hobbyist avoid at all cost to a welcome addition and/or helpful nutrient removal method for a system is quite a leap.  So let’s explore all of these things in a “Macro Algae series”! But first, here is a list of definitions to help the article make more sense to someone brand new to the hobby:

Algae – Google defines algae as “a simple nonflowering plant of a large group that includes seaweeds and many single-celled forms.  Algae contain chlorophyll but lack true stems, roots, leaves and vascular tissue”. uses “any of numerous groups of chlorophyll-containing, mainly aquatic eukaryotic organisms ranging from microscopic single-celled forms to multi-cellular forms 100 feet or more.  Formerly classified as plants, they have been divided into six phyla:  Euglenophyta, Crysophyta, Pyrrophyta, Chlorophyta, Phaeophyta and Rhodophyta”.  Before you click away, here is my definition:  “algae are the organisms that often look like plants, slime or hair, and grow in response to light and nutrients :).  I think my definition is best, but I wanted to be thorough!

microalgae chained together
Microalgae chained together

Microalgae – include small types of algae that can require a microscope to see.  These

tiny uni-cellular organisms float through the water column as phytoplankton, live in bentheic places (the substrate for instance) and are basically all throughout any body of water that contains nutrients and receives light.  They can connect to form the small stringy algae that we CAN see growing on the glass and out of rocks.  Microalgae take up carbon dioxide and sunlight through photosynthesis, and produce oxygen that benefits everything all of the other fish and organisms.  Cyanobacteria, dinoflagellates, and coralline are some of the common types of microalgae.



plant like macroalgae
Plant-like macroalgae

Macroalgae– Macros are the large, pretty, plant-like types of algae that grow under water and can be seen without a microscope.  Many aquarists use macroalgae to make beautiful display tanks, or in a refugium to control nutrients.  We will cover the different categories and uses of different types of macros in detail shortly.  Macros used to be considered “plants”, but the classification changed because even though they can create their own food through photosynthesis the way plants do, algae lack true roots, stems or leaves and live underwater….making them different in too many ways to be in the same definition.


Chlorophyll – The green pigment in all plants and algae that absorbs light for photosynthesis.

Photosynthesis – The process in which the chlorophyll within algae and plants use carbon dioxide and energy from light to feed/nourish themselves, and then use oxygen and “food” to release energy, creating carbon dioxide as a waste product.  Basically, it’s how algae uses light, nutrients co2 to grow.


The 3 ways algae are used in aquarium settings:

  1.  Refugium
  2. Reactor or Scrubber
  3. Display –

Here is the video covering the this topic: