7 Common Types of Algae Found in Freshwater Aquariums

It’s not easy being green… or brown… or red. How many different types of freshwater algae are you familiar with?


If you see something green and fuzzy growing on your tank surfaces, it is probably some kind of algae. Not all algae is green, however, and it might not all be fuzzy. There are a number of different types of algae which can be found growing in freshwater aquariums. Know your algae – here are seven different types of freshwater algae you might encounter and how to control them.


Related: Tips for Keeping Your Aquarium Water Quality High


Most Common Freshwater Algae Types


There are many different types of algae which grow in aquatic conditions but there are seven that are most commonly seen in freshwater aquariums. These seven types of algae are:


  • Brown Algae: This type of algae is most commonly seen in tanks with high phosphate or nitrate levels. Brown algae is also common in new tanks but it generally goes away after the tank has cycled properly.
  • Green Hair Algae: This type of algae grows in long, wispy threads and it is sometimes called thread algae. This algae is usually green in color, though it may also be brown. Hair algae is easy to remove but it quickly returns if the conditions responsible for its growth are not remedied.
  • Red Algae: This algae can be found in both freshwater and saltwater conditions and it is multicellular which gives it a rigid structure. Red algae is also sometimes called beard algae or brush algae but these are all different types of red algae.


Related: Setting a Schedule for Routine Tank Maintenance


  • Green Algae: This type of algae is most commonly seen in aquariums with very bright lighting and it can grow on tank objects as well as in the tank water. Sometimes green algae will cause an algae bloom which turns all of the water in the tank green.
  • Blue-Green Algae: Technically, blue-green algae is actually a type of bacteria called cyanobacteria and it is most commonly found in very nutrient-rich waters. Most freshwater fish do not eat blue-green algae but some freshwater snails like Nerite snails do.
  • Black Algae: This type of algae is commonly found in planted tanks and it grows in dark black spots that may be fuzzy in texture. Black algae is often seen in the roots of slow-growing plants and in filters.
  • Diatoms: This type of algae is brown in color and it may show up in spots on the walls of your tank or on other tank objects. Diatoms can be found in both freshwater and saltwater environments.


My Aquarium Has Algae! Now What?


If you notice algae growing in your aquarium, it doesn’t mean that you have failed your fish in any way. Algae is a natural and common struggle when maintaining a tank, one that we will all experience at one time or another. By recognizing that you have a problem, you’ve already taken the first step towards getting it under control. The earlier you recognize that you have an algae problem, the easier it will be to clean.


The Blackout Method


A common approach to removing algae in a planted tank, the blackout method works by removing all light from the tank for a set time. By removing light, you are removing one of the basic things that the algae need to grow and thrive.


Start by removing as much of the algae as you can from your tank. Complete a 50% water change, paying careful attention to thoroughly cleaning your aquarium filters. By taping standard black garbage bags onto your tank, completely block any light from reaching the aquarium and leave it in complete darkness for 96 hours. If you do use carbon dioxide in your tank, turn it off. You should also avoid feeding your fish during this time to avoid introducing any additional food for the algae.


After the 96-hour period, uncover your tank. Complete another 50% water change, cleaning your tank and all filters thoroughly. At this point, you should see a significant difference in the condition of your tank!


UV Sterilizers


Using a fluorescent bulb, these devices emit ultraviolent that can kill single-cell organisms like algae. They are safe to use around your fish when used correctly, continually working behind the scenes to keep the water in your tank clean and clear.


While these devices are found to be highly effective, it should be noted that they can only kill algae and bacteria that are floating in the water as it passes through the device. This means that they can’t completely clean your tank on their own. Instead, you should use a sterilizer as part of a larger cleaning plan, removing algae from the various surfaces in your aquarium and allowing the sterilizer to clean free-floating algae.


Chemical Algae Treatments


There are chemical treatment options available on the market that will work to combat the existing algae in your tank while also preventing any new growth. Take the time to read the packaging of any product that you are considering both to ensure that it is formulated to work with the specific type of algae that you are cleaning up as well as to learn how to use the product safely.


The benefit of using a chemical treatment is that it involves less work than physically cleaning and removing algae. However, not all chemicals are safe for use in every aquarium. Some chemical treatments that are labeled as unsafe for use in aquariums with live plants, snails, or other invertebrates. If these are included in your tank, be cautious. Always do your research first.


Tips for Controlling Freshwater Algae


The secret to controlling algae in your freshwater tank is to limit the things algae needs to grow. You cannot reduce your water level without affecting your fish, but you can take away other key nutrients like light. Algae is most likely to grow in tanks that are placed in direct sunlight and in tanks that have a surplus of artificial lighting. Keep your tank away from windows and only keep your tank lights on for 10 to 12 hours per day. You can also limit the nutrients that algae needs to grow – this includes nitrate and phosphate. Using an aquarium filter and performing water changes to keep the water quality in your tank high will help you to accomplish this goal. Another option is to stock your tank with algae-eating fish or invertebrates. Most species only eat green algae, but you can find species that specialize in eating certain types of algae if you do your research.


You may not be able to completely prevent algae from growing in your freshwater aquarium, but there are plenty of things you can do to limit its growth. By controlling lighting and nutrients you can reduce algae growth and adding algae-eating species of fish will take care of any leftovers.

Kate Barrington
Kate Barrington

Kate Barrington is the loving owner of two cats (Bagel and Munchkin) and a noisy herd of guinea pigs. Having grown up with golden retrievers, Kate has a great deal of experience with dogs but labels herself a lover of all pets. Having received a Bachelor's degree in English, Kate has combined her love for pets and her passion for writing to create her own freelance writing business, specializing in the pet niche.

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