All macroalgae operate the same, chemically. They all use light photosynthetically, absorb nutrients from the water (i.e., filtering), and grow biomass. Just like trees. The differences between types of macroalgae are in the physical structure of the macroalgae growth and the way the structure affects nutrient absorption speed. Here are the main differences as far as aquarists are concerned:

Chaeto: Pronounced KAY-toe. Chaeto is the nickname for Chaetomorpha, and it looks like a green dish-cleaning pad. It has no “roots” and thus does not attach to solid surfaces. It grows in saltwater only, and is not eaten by many fish.

Green Hair Algae: Includes Cladophora “angel hair” and Ulva “Easter basket” types. It has “roots” which attach to solid surfaces. It grows in freshwater and saltwater, and is eaten by almost all herbivores.

Slime: A solid algal growth, bright green to brown or black in color, that attaches to solid surfaces but not very securely.

Chaeto Reactor: A device that has water running through it, with chaeto growing in it. Also known as an “algae reactor”. A chaeto reactor does not allow air to enter; only water, and these reactors usually have a lid attached with screws to keep water in and air out.

Algae Scrubber: Also called a Turf Scrubber, or Algal Turf Scrubber (ATS). A device that allows air and water to interact to create a turbulent air/water interface like waves on a beach; it grows green hair algae or slime (depends on conditions) that attaches to solid surfaces.

Reactors and scrubbers are different from refugiums; a refugium is a space in a sump where macroalgae is placed, and a light is put over it. Refugiums have very slow flow, and very low light penetration, compared to reactors or scrubbers. You can modify a refugium to be a reactor, and with more mods you can make it a scrubber. But then it would no longer be a refugium.

All oceans, reefs, lakes, and rivers are naturally filtered. This means that algae does all the filtering of these waters. This is why algae is at the base of the entire aquatic food chain, and why algae biomass (phyto, benthic, etc) dwarfs the biomass of all aquatic animals combined. But for algae to absorb nutrients out of the water, the algae must grow. And to absorb nutrients faster, the algae must grow faster. Next we will look at what makes different types of macroalgae absorb nutrients differently.