Types of Algae

In this guide we are going to show you how to identify each type of algae, and what you can do to help grow the good stuff and avoid the bad stuff.
If you already know what type of algae problem you have, check out our guides on algae control & removal.

Types of Algae

How many types of algae are there?

Well, depending on who you ask, you will hear estimates ranging from 30,000 to more than 1 million types of algae found on Earth (how is that for consensus?) Whatever the exact number is, we know from AlgaeBase’s database of “135,121 types of algae” that there are a TON! But for aquarium owners, not all types of algae are created equal!

The Good, The Bad, and The Nuisance Algae…

While the Earth’s lakes, rivers and oceans depend on algae, some types of algae are toxic for marine life, and too much of the good stuff can lead to problems in any sized body of water. If algae growth gets out-of-control, the natural balance of the ecosystem can get thrown off resulting in sick or even a complete kill off from dead livestock, and if the balance gets thrown off by something else, that can cause the algae growth to get out of control! (grr!) So for the aquarium owner, we have to be constantly on the lookout for algae growth *while* managing the balance of the tank’s water and nutrients to prevent the algae from growing in the first place…

Know Your Enemies & Find your Friends!

Controlling algae can sometimes be a daily battle, and is always a source of frustration. Before you stress out too much, make sure you know how to tell the difference between bad algae and good algae, and how much is too much.

While you can find at least 30,000 types of algae around the globe, the most common type found in the home aquarium are red, brown, green or black in color and typically appear as a fuzz or hair like growth on rocks and tank surfaces.

Algae Blooms – a rapid increase in the algae population of a fresh or saltwater body. Algae blooms usually occur in tanks that have excess nutrients. Nitrate levels usually spike because of overfeeding and leftover food.

Black Algae – Is found in freshwater and planted tanks. It starts as black spot and can quickly take over a plant or tank. It is black in color and usually has a fuzzy look to it and can also be called brush algae.

Blue-green Algae – is a photosynthetic bacteria that can be unicellular or multicellular. Typically this algae builds up in surface waters or areas with low flow, but have been known to survive in almost any environment. In the home aquarium it tends to build up a greenish blue black or red film where the substrate meets the glass. It can spread across sand and rock very quickly. It has a slimy feel that has helped develop the nickname “Slime” and also can have a foul earthy odor. Even though it is called bluegreen algae it is actually cyanobacteria.

Diatoms – Of all the various species of algae, Diatoms are the most prolific and create most of the food for marine life to consume[1].  In your aquarium, they appear as small dots that show up on the sides of a tank and can sometimes be hard to scrub off. Most exist as a singular cell but can group together. They are typically brown in color and are found in fresh and salt water.

Green Algae – These algae are dark to bright green in color and show up on the glass and rock of fresh and saltwater aquariums. They can be a single cell or live in colonies and range in size. They can be free floating which turn water green or grown on rock or even shells of animals.

Hair Algae – Grows in long whispy threads, and can sometimes be called thread algae. Usually green or brown in color and can be easy to remove, but will return quickly if the cause is not taken care of.

Red Algae -Most red algae are multicellular and found in marine or fresh waters. Because off their rigid cell walls, they are an important building block of reef communities. Coralline algae is red algae that many aquarists enjoy having on the back wall of a tank.

Brown Algae – Usually found in tanks that have high dissolved nitrate or phosphate levels. Usually shows up in a new tank and can be cleaned away very easily. It usually goes away after a tank has matured and is also referred to as golden algae.



  1. This was very helpful! I will recommend this website to my friends for use.

    • I have a reddish, purplish algae that grows on my aquarium walls. My pleco can’t clean it, nor can my little magnetic scrubber.

      It grows super fast and will cover the aquarium walls within a week or two of cleaning.

      Water is testing fine.

      The only way to remove is to stick my arm in the tank and scrape it off with an old credit card.

      Any thoughts or help? If I even knew what kind it was, I could research how to remove…


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