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Aquarium Algae Types

aquarium algae home & habitat

You’ve got your aquarium all set up and cycled. You’ve added some beautiful fish, colorful accessories and even live plants. The filter is running and the temperature is within range. Yet you notice a brown film on your substrate or patches of green on your rocks—this is aquarium algae. Whether it’s common types of freshwater algae or various saltwater algae species, every aquarist has to deal with this persistent aquatic organism. So is algae bad for an aquarium? How can you get rid of it?  Read on for answers to these questions and more.

What kind of algae is in my aquarium?

The first step to addressing algae in your aquatic habitat is familiarizing yourself with the different aquarium algae types and learning how to identify them. There are four common types of algae that affect both saltwater and freshwater habitats and several more common saltwater aquarium algae types. 

Green hair algae

green hair algae

Green hair algae is one of the most common types of aquarium algae in both saltwater and freshwater habitats. It can grow in clumps of short, fluffy hair-like fibers or cover surfaces with strands up to two inches long. In any form, green hair algae are a bright green color and look a lot like a soft grass—and can be just as difficult to eradicate as the weeds in your lawn might be.  

Green spot algae

green spot algae

Green spot algae appear as bright green, circular patches on the sides of your aquarium or on accessories like rocks and coral. A little bit of spot algae in an aquarium is common and isn’t typically harmful. However, if the spots begin to grow, you’ll need to scrape off this hardy aquarium algae type by hand and make adjustments to prevent it from growing back. 

Brown algae 

brown algae

Brown algae in aquariums are common and can thrive in low-light conditions. Also known as diatoms, it’s typical to find brown algae in newly set up aquariums that haven’t completed a nitrogen cycle where beneficial bacteria are not yet established. Brown algae initially looks like a thin film on the surfaces of your habitat and can quickly get out of control.  

Blue-green algae

blue green algae

This isn’t actually an algae, but it behaves similarly and is often grouped into this category. Blue-green algae in aquariums are actually photosynthesizing bacteria that also feed off the nutrients in your habitat. It appears as a fast-growing, slimy film that can be blue, green or even brown.  

Red slime algae

red slime algae

While red slime algae can be found in freshwater, it is a much more common saltwater aquarium algae type. Red slime algae are cyanobacteria, the same as blue-green algae. In saltwater, this organism can appear not only as blue or green but also red, purple and black. Red slime and blue-green algae both have one thing in common—the presence of these cyanobacteria is a sign of an imbalance within the aquarium and should be dealt with immediately.   

Coralline algae

coralline algae

Coralline is a red calcareous algae belonging to the division known as Rhodophyta. Unlike red slime algae, it is a true algae that can be good for your habitat. This type of algae in marine aquariums appears as a hard, pink, red, purple, blue, yellow or green crust on your aquarium walls, rocks, decor and substrates. Along with the gorgeous colors this algae produces, it can also help encourage the growth of stony coral. If you have a reef aquarium, you should consider promoting the development of coralline algae. 

Bubble algae

bubble algae

This is a particularly common marine fish tank algae type, as it  grows in tropical and subtropical ocean waters around the world. Bubble algae look just as their name implies—they are green, shiny bubbles that appear anywhere from a single bubble to tightly packed bunches on the base of your coral and other hardscape décor. Like coralline algae, they aren’t necessarily bad for your aquarium if they are properly managed, but they can grow out of control quickly and start to cause issues. In fact, they can even compete with coralline algae for space. 

What algae is bad for fish?

Blue-green and red slime aquarium algae aren’t algae at all, but rather bacteria that produce a toxin that can be deadly to aquatic life. Many other types of aquarium algae can benefit fish by acting as a natural food source and filtration device—but they must be kept under control.  

Like other plants, all true aquarium algae types engage in photosynthesis. They consume carbon dioxide during the day but then release carbon dioxide at night, which can lower the pH in your aquarium. Thus, too many algae in your habitat can create an unhealthy fluctuation of pH. However, the main problem isn’t usually the algae itself, but that algae overgrowth indicates poor and imbalanced water. Many types of algae are also simply unsightly, covering your beautiful coral and decor, as well as the walls of your aquarium, making it difficult to see your aquatic life.  

That said, some algae are good for your habitat—especially certain marine aquarium algae types. Finding the right balance between coralline algae and other beneficial algae types can help a marine habitat thrive.  

What causes aquarium algae?

Different types of aquarium algae thrive in different environments. However, the root cause of most algae is the same—an imbalance of lighting and nutrients in your habitat. There are three factors that often cause this imbalance.  

Too much light- Because they use photosynthesis, the most common types of algae in freshwater aquariums and saltwater habitats need light to survive. However, providing too much light to your aquarium can be problematic. Using an artificial light that is too strong or leaving it on for more than ten hours per day are common causes of algae growth in aquariums. Algae also love natural sunlight—you should not place your aquarium near skylights and windows that receive direct sunlight. 

Overfeeding- It’s incredibly easy to overfeed your aquatic life.  When you overfeed, uneaten food falls to the substrate in the bottom of the aquarium and begins to decay, releasing ammonia, nitrates and phosphates into the water. Overfeeding your aquatic life will also lead to more waste, which creates ammonia and even more nitrates. And if there is one thing to remember about the different types of aquarium algae—they all love to feed on nitrates and phosphates.   

Poor water quality- To keep your water in good shape for your pets, you need to perform 10 - 20% water changes every two to four weeks, depending on the size of your habitat and the amount of aquatic life. Smaller aquariums typically require more frequent changes, as waste will build up more quickly. Before adding new water, use the appropriate  to remove any ammonia, chlorine or chloramine. You can also pretreat the water with additives that break down the nutrients that aquarium algae consider food.   

How can I get rid of aquarium algae?

An ounce of prevention is always worth a pound of cure—but what if you already have algae overgrowth taking over your habitat and you need to do something now? What is the fastest way to get rid of aquarium algae? The short answer is you’ll need to scrape it off. Use a scraper on the sides and flat surfaces of your aquarium, removing accessories and scrubbing them with a sponge or toothbrush. You can also soak accessories in a 3% bleach solution, but be sure to rinse them thoroughly or soak in clean water with a dechlorinator and let them dry.  

What if you just don’t have the time to address algae concerns in your aquarium? Will algae go away on its own? Some aquarium algae types—like brown algae—may go away on their own, but others—like green algae—will not. You’ll need to restore your habitat’s conditions to a balanced state to eliminate algae for good. There are commercially available algaecides that can help when other methods don’t.  

What are the best aquatic algae eaters?

Aquatic algae eaters can not only help get rid of algae but also maintain a thriving habitat in other ways. Plecostomus are one of the most well-known freshwater algae eaters—however, some species can grow to sizes from 12 to 24 inches, making them too large for smaller home aquariums. Smaller fish—like Siamese algae eaters and otocinclus catfish, as well as some types of snails and shrimp, are good choices for habitats ranging from 5 to 25 gallons.  

There are a variety of aquatic pets that will eat saltwater aquarium algae types. Fish like angelfish, tangs and foxface rabbitfish are known to nibble at algae but require a large habitat—about 70 gallons or larger. Tailspot blennies and sailfin blennies are two algae eaters that can thrive in about 30 gallons, and some species of gobies are ideal for nano reef habitats of 10 gallons. For smaller aquariums, you can also look beyond fish—shrimp, crabs, snails and urchins can do an excellent job of clearing various types of algae in marine aquariums.  

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Reviewed by Dawn Burch, Director of Animal Care, Education and Compliance (ACE) Team

Dawn is Petco’s Director of Animal Care, Education and Compliance, leading a team that supports animal care operations, regulatory compliance, learning and development, veterinary relations and more. She is passionate about animals and committed to improving the lives of our companion animals, aquatic life, guests and partners.