January 4, 2022 9:21 pm


What are Marimo moss balls?

Marimo moss balls are also known as Cladophora balls, moss balls, or lake balls and are a rare growth form of green algae in which the algae grow into large green balls with a velvety appearance.

Green moss Ball

The most common places to find most balls are in a number of lakes and rivers in Japan and Northern Europe. Their population has been declining in the last few years and they are also a household favourite pet. Yes, you read that right, the Marimo moss ball is very popular with plant lover and is usually kept at home in water with other plants, fish or in a terrarium of it's own. There are plenty of benefit in having a moss ball from providing oxygen to the water to help prevent excess algae growth or not to mention the very low maintenance requirement. They can be kept in a variety of different habitats, including a bowl, vase, Jar, terrarium or fish tank. You can also learn about Marimo Moss Balls history by cheching out our latest blog post on the topic.


How do you keep your moss ball alive?


In their natural environment, Moss balls form at the bottom of lakes and do not need direct sun light to grow. In you keep them at home, avoid direct sun light but make sure they do get some light to enable them to keep their beautiful green colour. Direct sun light may result in your moss balls turning brown.

Sunlight for marimo

Changing the water:

Regular tap water can be used here in the UK, you will need to change the water every two weeks for best results, allowing the water to rest for 24 hours prior to changing the water. When comes the summer, you may have to change it more often to keep you marimo moss ball healthy.

Water for moss balls

Moss balls and salt:

Marimo moss ball will tolerate salt and can be used in salted water tank. In fact, adding salt to your aquarium or terrarium is a recommended solution when your marimo moss ball is morphing to a brown shade. They actually do grow in salty water conditions in Japan. The thickest marimo moss balls were found to be where dense salty water from multiple natural springs runs together to join into a lake. Ideally the salinity should be just around 1.010-10.020sg. If the ball starts losing colour, lower the salinity by doing a partial water change or adding distilled water.

Salt for moss balls


Marimo moss balls prefer colder temperatures ideally between 17°C and 23°C and might not be suitable for tropical fish tank. If it gets too hot in the summer, you can always add an ice cube to the mix.

Temp for moss balls


What are Marimo moss balls common problems?

Brown patches:

Your Marimo moss ball is getting dirty need to be washed. To fix, remove the moss ball and rinse it under tap water then if you can try to dip it in dechlorinated water.

Brown on one side:

Your Marimo moss ball is not getting enough light. To fix, you need to often turn your moss balls around to make sure the get enough light all the way around.


You moss ball is getting too much light. To fix, simply move you moss balls to a different location or if you have an aquarium, reduce the light.

White spots:

Your moss balls has a parasite. To fix, you will need to clean your Marimo moss ball very well as per the instruction in this blog post.

Slimy green:

Your moss ball is covered by another algae. To fix, you will need to clean your Marimo moss ball very well as per the instruction in this blog post.

Black moss ball:

Your moss ball is dying. To fix, remove the black portions and roll your Marimo back into a ball. Then clean as per the instructions in this blog post.

Lots of marimo moss balls in a bowl with water


How to clean your moss ball:

Take the moss ball out of the water and gently squeeze your Moss Ball to flush out any dirt trapped in it. If your moss ball has white, black spots or slimey green, remove them gently. You may also gently roll your Moss Ball back and forth on your palm to help them retain their round shape. Once you’ve done that, rinse them under clean tap water and squeeze and shape into a ball again. When you’re done, simply put them back in clean water. You should clean you moss balls every 2 weeks if you can.

Close up of marimo moss ball in water with bubble


What size are marimo moss balls?

Moss balls are known to grow up to 20 cm and, in the right conditions, they can surpass this expected growth rate. The world's largest and oldest marimo moss ball is said to be 93 cm in diameter. To reach this size, the moss ball would be about 200 years old.

Marimo moss ball size check



Are Marimo legal in the UK?

Yes, Marimo moss balls are legal in the UK where the supply chain is controlled, but not in the US where there is currently a ban on selling Marimo moss balls because of contamination with invasive zebra mussels. These mussels are an invasive species that have caused economic and ecological damage, and populations are difficult to eradicate once they are established.

Legal marimo moss balls


Can Moss Ball Pets survive in a fully covered bottle?

Yes, Moss Ball Pets can survive in fully covered bottles. In fact closed bottles can keep out the dust and other pests that may harm your pet! Check out our Marimo moss ball terrarium in our shop.

Moss Ball in terrarium with white gravel


Why are my Marimo moss balls floating?

As part of its photosynthetic process, it produces tiny oxygen bubbles.  Some of these bubbles get trapped inside it, causing it to float.

Moss ball in water


Can I have shrimp with my Moss Ball Pets?

Shrimp love to graze on moss balls and will pick at them, however beware that Amano shrimp have been known to tear up moss balls. Overall they are a good addition to your shrimp tank and do nothing but benefit the aesthetic of your tank.


Will Moss Ball Pets reproduce?

Yes, Marimo will reproduce when they are kept in a large pool of water. If that happen, you would see a bump growing on them.


How Quickly Do Marimo moss ball grow?

Marimo balls grow very slowly, up to 5 mm per year, eventually reaching 5 to 10 cm in aquariums, or 20 to 30 cm in natural conditions. Wild Marimo moss balls live in cold, dark waters where the waves slowly turn them to expose all sides to the light which they need to grow.

In shops or online UK shop like ours, you will usually find moss balls to buy with a diameter of 2 to 6cm.

Green marimo moss ball in hand


Do Marimo moss balls need food?

Moss Ball Pets require water and very minimal light source to survive. It does not require feeding as it performs photosynthesis just like a plant.

Molten glass on wood with marimo moss ball


Are moss balls animals or plants?

Have you ever wonder if moss balls are real amimals or plants? Moss Ball Pets are unique living organisms and yes, they are alive. People actually keep them as a pet in aquarium or small jar. Are you ready to get your own Marimo moss ball pet? Visit our shop to get started. You can also try our Moss Ball name generator to give a new life to your Marimo pet.

Have some fun and test your Marimo moss balls knowledge with our fun quiz.

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