Marimo Moss Ball Aquarium – A Complete Guide

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Moss balls, also known as aquatic moss, are a unique addition to any fish tank. Not only do they add color and interest, but they also provide an important function in the tank by filtering the water. If you’re thinking of adding a moss ball to your aquarium or wanting a moss ball aquarium we have you covered. We will go over care tips and environment. Read on for everything you need to know!

Key Takeaways

  • Marimo moss balls are a unique type of algae rarely found in the wild.
  • This algae has a unique spherical shape that it gets from being rolled around by gentle currents in its natural habitat.
  • Marimo moss balls require little to no extra care in the aquarium and can be kept in hotter or cooler temperatures.
  • Marimo balls can live extremely long lives but have a very, very slow growth rate!

A Brief Overview Of Moss Balls

Scientific NameAegagropila linnaei
Common NamesMarimo moss balls, Moss balls, Cladophora balls, Lake balls
OriginJapan, Iceland, and regions of Northern Europe
Skill LevelVery Easy
LightingLow to Moderate
Tank PlacementBottom of tank
Flow RateLow
Temperature Range65 – 80°F
Height<5 inches in diameter
pH Range6.5 – 7.0
Growth RateSlow
Feed TypeWater column feeder
Co2 RequirementNo


Marimo moss balls can be found for sale at most aquariums and pet stores. They can usually be found sitting idly on a shelf in a small container of water, sometimes next to the selection of betta fish. Fortunately, marimo moss balls can withstand these conditions, unlike their betta fish counterparts.

Marimo moss balls are one of the most interesting yet understated living things you could add to your aquarium. We call these little green balls living things because they don’t quite fit into any other category of fish, plant, or even coral. In fact, moss balls are a type of algae.

The marimo moss ball is a species of filamentous green algae called Aegagropila linnaei. Their common marimo name originates from Japanese meaning water plant and bouncy ball, which perfectly summarizes its appearance and texture. Though the second part of their common name is moss, this is a misnomer that tends to sell better than an algae label. Even though the marimo moss ball is technically an algae, many hobbyists still refer to them as aquarium plants.

While marimo moss balls are very common to find in the aquarium hobby, their populations are decreasing in the wild. Habitat destruction and dredging have disrupted the bottoms of lakes where these balls are found while eutrophication–or the accumulation of excess nutrients–has led to excessive algae growth and subsequently limited photosynthesis. All this combined has left marimo moss balls to starve.

Compared to other plants, marimo moss balls were discovered a long time ago. These algae balls were first discovered in the 1800s on the floor of Lake Zeller in Austria and then later in Japan1. They only just rose in popularity in the aquarium hobby over the past decade.

Are They A Type Of Pest Algae?

For a while, marimo moss balls were scientifically categorized as Cladophora aegagropila. If you’re familiar with algae taxonomy, then some red flags might be going up!

How Does Marimo Moss Ball Look Like

The Cladophora genus is notorious for housing some of the most frustrating algae species known to the home aquarium. Species of this algae have a similar filamentous texture to marimo balls but grow very quickly and in an unorganized fashion in comparison. It can be very easy to confuse this pest algae for a rogue marimo moss ball but scientists were able to find definitive differences between the Cladophora and Aegagropila genera.

So, no. Marimo moss balls are not a type of pest algae, though they are still a species of freshwater algae. If you find green algae that happens to look like your moss ball is spreading across the tank, then you’re most likely facing a Cladophora algae problem.

Cultural Significance

The marimo moss ball is a very important part of Japanese culture. So much so that it was deemed a national treasure that brings good luck and fortune. Marimo balls may also be given to each other’s significant partner as a way of expressing the heart’s true desires.

Are They Good For Fish Tanks?

We’ve said it before and we’ll say it again, algae isn’t inherently bad. In fact, algae is a necessary component of both freshwater and saltwater ecosystems by providing food for fish and invertebrates while also taking and storing nutrients out of the water column. In the same way, marimo moss balls are beneficial for freshwater fish tank setups.

Marimo moss balls aren’t the most efficient plants you can have in your aquarium, but they’re better than nothing. Aquarium plants depend on nutrients that are available in the water column to grow. These nutrients come from water changes, fish waste, and other organics that enter the system. Plants and algae can then use these nutrients to grow.

However, marimo moss balls have an extremely slow rate of growth, which means that they don’t need nutrients often. Still, they are processing excess nutrients that would otherwise need to be converted by beneficial bacteria or manually removed.

At the same time, marimo moss balls also introduce fresh oxygen into the aquarium through photosynthesis; fish and invertebrates create carbon dioxide which can then be used by the algae to create their own food. Freshwater shrimp and snails also appreciate grazing on any waste and detritus that gets stuck on the marimo balls.

Do They Keep Fish Tanks Clean?

A marimo ball will not outcompete other more advantageous species of plant or algae. These are slow-growing algae that fail to thrive if overcrowded. So unlike some other species of fast-growing plant that can be used as biological control, a marimo moss ball will not help to remove enough excess nutrients to the point where other algae fail to grow.

How Long Do They Live In A Fish Tank?

A very long time. The oldest known marimo ball is about 200 years old and it is unknown how long they can actually live. These algae will continue to live and grow as long as some basic conditions are met. On top of that, marimo moss balls are very hardy and will adapt to most imperfections and sudden changes in their environment.

Origin And Habitat

Marimo moss balls are rare to find in the wild and need pretty exact conditions. They prefer cooler temperatures, slower currents, and low light; other species of plant and algae must also be limited so that the marimo balls are not out-competed.

Marimo balls are native to Japan, Iceland, and regions of Northern Europe. They have also been found in North America and Australia, but are not considered to be native to those regions.

Marimo moss balls usually live on the bottom of freshwater lakes, but can also be found attached to rocks or free floating. They are most likely to be found in their unique circular shape while on the lake floor where they are gently rolled by tides and currents mostly caused by wind action.

As mentioned before, the wild marimo moss ball population has been on the decline for many years due to habitat destruction and eutrophication.


There is nothing else that quite looks like a marimo moss ball. In the wild, marimo balls can have a perfectly rounded shape thanks to the gentle current on the lake floor. In the aquarium, hobbyists cant gently roll their moss balls from time to time to keep this shape intact.

Marimo balls are green algae that are made up of small individual strands. There is no core. Together, these strands make a compact ball that ranges in size from 2 inches to a foot in diameter. Most aquarium marimo moss balls stay under 5 inches in diameter, which takes a very long time to accomplish.

Hobbyists should not confuse a marimo ball with a floating Christmas moss ball. These two balls are very similar in appearance and are often sold from the same fish tank. Christmas moss balls are covered in Christmas moss (Vesicularia montagnei), a true freshwater aquarium plant. Christmas moss has long, light green, fuzzy individual strands that take a Christmas-tree shape upon closer inspection. These balls are able to float as there is a buoyant core in the center.

How Fast Do They Grow?

Marimo balls are very slow-growing, but how slow is slow? On average, marimo moss balls grow 0.20 inches every year. That means 1 inch every 5 years. Now, recall that these algae can grow to 12 inches in diameter!

What Maes A Good Tank Mate For Them?

Moss balls are the perfect addition to both coldwater and tropical fish tanks. Here are just a few fish species that this aquarium algae are perfect for:

In general, any fish that can be kept with true freshwater plants can successfully be kept with marimo moss balls. Freshwater shrimp and snails will also especially love foraging on and around marimo balls as food and detritus get stuck.

A marimo ball is also a great alternative to other live plants for small betta fish tanks. Some betta fish like to pick at plants, but will generally ignore marimo moss balls.

Fish Species To Avoid

We mentioned that a marimo moss ball is a great addition to a coldwater setup, like one designed with goldfish in mind. Goldfish will love to nip at their marimo ball, pushing them around the tank to help keep their round shape. However, that curiosity and fun can quickly turn into an appetite. For this reason, we recommend using caution when introducing a moss ball into a goldfish aquarium.

For the same reason, use with cichlids should also be watched. Many cichlids like to move the decorations in their homes around, which can help keep a moss ball round but can also become food or destroyed over time.

Other species to avoid with marimo moss balls are plecos and crayfish.

Are They Harmful To Fish?

It is true that some species of algae can be harmful to fish and invertebrates, especially when eaten. However, there is no known toxicity or lethality associated with Aegagropila linnaei, making them perfectly safe to use with fish and invertebrates!

Feeding Moss Balls

Moss balls are very undemanding. They do not require a lot of light or nutrients.

In general, feeding your moss ball is unnecessary. As long as there are available nutrients in the water from fish waste and other organics, there should be enough food in the water column for your moss to survive. For this same reason, carbon dioxide injections are also not needed.

If you’re placing your moss ball in a heavily planted tank, then you may want to dose liquid or dry fertilizers to help keep nutrients available for the slower-growing species.

How Much And How Often To Feed

How much and how often you feed your planted aquarium with fertilizers is dependent on how nutrients move throughout the system. If you find that you have low nitrates, generally considered under 10 ppm for a planted tank, then you may need to dose supplements to keep nutrients available.


Marimo moss ball care is simple and straightforward. In fact, your algae ball might be even easier to keep alive than some pest snail species.

There are a few conditions that need to be met to keep your marimo moss ball happy and healthy, though.

What Do They Need In Their Tank?

Marimo moss balls don’t need to be kept in a conventional planted tank with strong lighting or carbon dioxide dosers.

In fact, many people keep marimo moss balls in glass jars on their bookshelf without any substrate, filtration, or air movement; some rerolling and water changes may be needed from time to time. The only requirement is that they are constantly submerged and exposed to low to moderate lighting for at least 7 hours a day.

Marimo moss balls can be kept on a gravel or sand substrate or on a bare bottom. They are most commonly kept on the bottom of the tank, but they can be attached to rock and driftwood as well.

Otherwise, marimo moss balls don’t even need to be kept with fish or invertebrates and can be used for household decoration!

Planted Tank Parameters For A Tank

Marimo balls do not need any special water parameters. They are very hardy and can withstand fluctuating parameters and temperatures as long as they aren’t stressed too much.

That being said, this aquarium algae does best when kept in a cooler area of the home or in a coldwater or tropical setup. The water temperature should remain steady between 65 and 80°F. When kept with fish, pH should remain fairly neutral around 7.0 with 0 ppm ammonia and nitrite and minimal nitrates.

Marimo moss balls should also be kept in dechlorinated water, no matter if kept in a jar or in a fish tank. Water dechlorinators and cheap and easy to use.


Marimo moss balls live on the lake floor where sunlight struggles to penetrate. This means that, in the home aquarium, lighting does not need to be strong either. Marimo balls do best when grown under low to moderate lighting. Too much light can cause the algae to burn, which will cause discoloration. Not enough light may cause the algae to grow looser and turn brown or white as well.

If keeping a marimo moss ball without artificial lighting, then it’s important to make sure that it is getting enough light to photosynthesize. This usually means indirect sunlight for at least 7 hours or more.

It is also important to remember that the bottom of the marimo moss ball needs to get sunlight too. To help prevent brown spots from forming on the underside of the ball, the moss ball should be rotated about every week or so. Many hobbyists do this during their weekly water change schedule.


Marimo balls do not require filtration, though it’s strongly recommended to use a sponge filter or hang on the back filter. Canister filters can be overly strong for your moss ball.

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If you decide not to use filtration when keeping marimo balls, then regular water changes will be needed to keep the water healthy.


When it comes to keeping marimo moss balls, flow is more important than filtration.

The ideal water flow for a moss ball would be gentle and random. This would imitate the light currents found at the bottom of freshwater lakes that help keep this algae rounded. Unfortunately, this isn’t really possible in the aquarium unless filters or an air stone are hooked up to a timer.

The best way to imitate these conditions is by placing the moss ball near a filter or air bubbles so that the ball is gently rocked back and forth. This helps bring water movement under the moss ball and slowly turns it over.

If this is not possible, then you will need to manually reshape your marimo ball from time to time.

How To Keep Them Round

Marimo balls are popular due to their minimal care requirements and unique round shape. Unfortunately, this algae doesn’t naturally grow in a spherical shape and depends on environmental factors to round it out.

Luckily, it’s easy to keep your moss ball in shape. Every couple of weeks, simply remove your marimo ball from the water and roll it around in your hands. It should easily return to its compact shape.

At the same time, it’s recommended to gently squeeze out your moss ball with old aquarium water. Detritus easily gets stuck in marimo balls and rinsing them occasionally can help remove some of this waste.

How To Propagate

In all honesty, it is usually easier to buy another moss ball than it is to propagate one that you already own. This is because of how long it takes for this algae to grow.

The easiest way to propagate marimo moss balls is by cutting them in half and reshaping the new pieces into spheres. It may be necessary to use thread or fishing line to wrap around the new pieces until they hold their shape on their own.

The problem is that it will take years for both these new pieces to reach the size that the original piece was. Because of this, it’s recommended to buy an entirely new marimo moss ball of similar size instead.

Introducing Them To The Tank

Introducing marimo balls into the freshwater aquarium is easy, though it wasn’t so easy a few years ago. In 2021, zebra mussels (Dreissena polymorpha), small invasive freshwater mussels, were discovered living inside store-bought marimo balls. Luckily, the problem was caught early on and infected marimo balls were recalled.

To safely introduce your marimo ball into its new tank, first, rinse it off with old tank water. This will help remove the tank water from the store, which could possibly contain unwanted chemicals and pests.

Next, place the marimo moss ball in its desired location. It may float in the water column for a couple of days until it becomes waterlogged. You may tie it down or wait for it to naturally settle.

And that’s it! With some regular rinsing and reshaping, you will have your marimo moss ball for decades.

Health And Disease

Marimo moss balls are very hardy and resilient to internal and external stresses. However, they can start to develop white or brown spots if there is too much or not enough lighting.

Signs Of Health

A healthy marimo moss ball will be fuzzy and bouncy. The dark or bright green coloration should be even across the surface. This algae should be easy to mold into a circular shape, but firm enough that it holds its own in the water.

Signs Of Ill Health

A struggling marimo ball may be brown, yellow, or white. This is usually indicative of a lighting issue instead of a nutrient problem.

If your marimo ball develops discolored spots on one side, make sure that lighting is even across the surface of the ball. Discoloration can either mean too much or too little light. It can also mean that the ball has been on one side for too long.

In time, this discoloration will grow out on its own. If there is not a large area present, then the marimo ball may be trimmed once placed in better conditions.

Where To Buy

Marimo moss balls may be conveniently found at your local fish or pet store. They are often sold in little cups near other fish tank decorations or near the betta display. If your store of choice does not carry them, they can easily be bought and shipped through online stores.

Marimo Moss Balls

An easy to keep and hardy aquarium plant. They are small and fit in any aquarium setup. Provides good food source and will soak up nutrients

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On average, small moss balls retail for about $5. Larger ones can cost upwards of $15.

Final Thoughts

Marimo moss balls aren’t like other aquarium plants, in fact, they’re not considered plants at all. This unique algae is rare in the wild but has become a staple for coldwater tanks and betta fish setups. Moss balls require little to no extra care but need to be rerolled every once in a while to maintain their circular shape.

If you don’t feel like adding marimo balls to your fish tank, then you can even keep them in glass jars around your home as decoration!


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