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Marimo Moss Ball: Betta Fish, Benefits & Care

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Common Names: Marimo, Mossimo, Moss Ball, Seaweed Ball, Algae Ball, Japanese Moss Ball, Lake Ball, Marimo Moss Ball
Scientific Name: Aegagropila Linnaeii
Growth Rate: 5 mm (0.2 inches) per year
Life Span: Over 100 years!
Reproduction: Propagation is most common

A marimo moss ball is a filamentous green algae that’s naturally found in Iceland, Japan, Scotland, Estonia and most recently, Australia. Despite some of their common names among aquarists, they are not moss at all. They do not affix themselves to anything like other species of moss. Moss balls were first discovered in the 1820s and are even a protected species in Iceland (Lake Myvatn) and Japan (Lake Akan). Lake Akan is home to some of the largest marimo on the planet, reaching up to 30 cm (11.8 inches).

Moss balls are solid spherical balls of dense algae and do not have a solid core to them. They create their own food through photosynthesis and are extremely easy to care for. Best of all, moss balls will not turn your tank’s water green like other forms of unwanted algae. With that said, make sure you don’t add any algae killing chemicals to your aquarium. There are lots of benefits to keeping marimo as a tank mate, especially since they don’t produce any waste.

Marimo Moss Ball for Betta Fish

Moss Balls for Betta Fish

Betta fish and moss balls can live in perfect harmony. Aside from their natural velvety-green splendor and contrast amongst other decor, betta fish love playing with and resting on marimo moss balls. One minute it’s a velvety couch and the next it’s a soccer ball to push around. Ghost shrimp and aquarium snails, other common betta tank mates, are also big fans of the moss ball because of its ability to harbor small particles of food for feasting.

Marimo moss balls can live in the same water parameters that bettas thrive in, however they do grow faster in colder temperatures. When they are fully saturated with aquarium water they will sink to the bottom and only move from being disturbed. Moss balls also work to retain good tank bacteria, emit oxygen, and reduce nitrate levels which can stress betta fish health at high levels.

Marimo Moss Ball Care

Caring for your moss ball is very straightforward under normal conditions and health. They are basically indestructible and will only need occasional maintenance. In clean water and if cared for properly they could live longer than you.

Food

Wondering whether moss balls need extra fertilizer or food? Nope, they make their own through photosynthesis using natural or artificial light.

Shape

Moss balls are cool because they’re round living balls of algae right? If a marimo moss ball stays on one side for too long it may start to flatten and you don’t want that. Simply place it on a different side or roll it gently in your hands to reshape it like you would a meatball.

Lighting

Moss balls naturally inhabit the cool depths of lakes and receive minimal indirect light. You should mimic this environment for a healthy marimo. Keep moss balls in shaded tank areas and out of direct sunlight. Overexposure to light will lead to browning or brown spots, especially if the water gets too hot. Rotate to another side if browning is occurring from too much light.

Water Changes and Cleaning

Each time you perform a water change or fully clean your betta’s tank you should also inspect your moss ball for signs of browning or loss of color. In a container of aquarium water, squeeze the moss ball slowly allowing it to expel the water and then become resaturated.

Repeat this process several times. Think of this process like cleaning a household sponge. This will clean the moss ball and remove all of the dirt and bacteria that it has trapped over time. Brown or grey coloring is a sure sign of a dirty moss ball that is ready to be cleaned.

Sick Marimo

A healthy moss ball will be a deep and bright green color with lush outward filamentous growth. White or grey in color indicates too much light, brownish can indicate too much direct sunlight or a dirty moss ball, and black spots mean decay (remove them by cutting them out). For treatment you can also quarantine moss balls and add aquarium salt and colder water to promote health and growth.

Moss Ball Reproduction

Moss balls can reproduce in two distinct ways: naturally or forced. Growing at only 5 mm per year, marimo can take a long time to get large enough for reproduction. Natural reproduction involves a small lump starting to grow off of the existing marimo which will eventually fall off and grow on its own.

If you have a larger moss ball however, you may want to propagate it by squeezing all of the water out of it and dividing it in half or even thirds or quarters depending on its size. To promote circular growth you should continue to rotate it in the tank and carefully roll it in your hands occasionally.

Where to Buy Moss Balls

You can buy marimo moss balls in a lot of the same places as you can betta fish. Look in big pet stores like Petco and PetSmart, aquarium forums, local aquatic stores, and online. Moss balls that are not housed with other fish or plants are usually best if you don’t want to quarantine them before adding them to your betta fish’s tank. When buying them in person make sure to inspect for signs of health (e.g. bright green color).

If you’re buying a moss ball online, make sure it is from a reputable source and it’s in fact a real marimo moss ball. Fake ones do not provide much benefit aside from being visually appealing. Always check the description for size too as they can range from 0.5 inches to 5 inches or more, and will be more expensive the larger they are.

FAQ

Are there fake moss balls?
– There are fake moss balls sold online and in pet stores. Fake moss balls are usually plants wrapped around a solid plastic or other material core. They are usually perfect spheres and do not have the lush appearance of a real marimo moss ball.

Why is my moss ball floating?
– Moss balls will float if they are not saturated with water or if they have an internal air bubble.

What does marimo mean?
-Translated in Japanese, Marimo means ball seaweed.

Still have a question or just want to share your experiences with marimo moss balls and betta fish? Share them in the comments below!

41 thoughts on “Marimo Moss Ball: Betta Fish, Benefits & Care”

    • Yes, Jenny, it should be okay. If you notice it starting to brown, move it to a place that has more shade in the tank.

  1. Hi, I have a betta fish a year ago, since I have had fungi, I have tried several products and remedies that used to and works a lil but a few days ago my fish has white fungus, is long down the tank or on the surface, is swimming slower, does not eat well, I do not know how to help him, when they have fungi suffer? Can I do something to help him?

  2. Had to remove the filter from my 2.5 Betta tank. My 1 1/2 year betta was getting stuck. Would a Marimo Moss Ball be a better choice. I have no alge problems.

    • Yes, a marimo moss ball would work to remove a little bit of the waste produced. Just keep up on your water changes for that size tank and you’ll be fine. Consider getting some test strips to test for pH and ammonia levels in between water cyclings if you’re concerned.

  3. My daughter had a couple of marimo balls in her tank and after a year or two they seemed to grow and algae was everywhere in the tank. Would this be from the balls or possibly other algae?

    • It shouldn’t be from the moss balls, they help to clean the water. If it’s brown algae the tank might not be getting enough light during a 24-hour cycle, and if it’s green algae, the tank might be getting too much light or sunlight.

  4. Thank you for this information…I noticed that my beta bowl water was smelling more even with weekly water changes… I smelled the algae ball and it didn’t smell very good and I was tempted to throw it out even though it was nice and green. I read your care info and did what was recommended… squeezing and dipping back into the water several times… the smell went away… I didn’t know that it could be squeezed or handled so much! Thanks… you made my beta happy!

  5. Will I have to feed my betta fish if I put the moss ball in my tank. I have a double tank where one flows into the other and I have to put extra food into the tanks because it filter to fast for the bettas to eat and this is makin my water very dirty very fast. I am wondering if I could use the moss balls as a source of food for my betta.

    • Betta fish do not eat moss balls. They need a healthy source of protein as they are primarily carnivores which is provided through high-quality pellets specifically for betta fish. You could, however, turn the filter off during feedings.

  6. Are moss balls simple to introduce? I’ve read so much about betta fish, and that they get stressed from the slightest changes. So I’m just wondering if there’s a process. Or do I just add it and relax?

    • Take some of his tank water and place it into a different container. Place the moss ball in the tank water, and give it several good squeezes. This will clean the moss ball and also re-soak it with the tank water your betta is used to. Then add it in and relax!

  7. We have a small tank (1.5 liters) with a moss ball and a beta. We’ve noticed a clear coating on the top of the water – even with weekly cleanings it comes right back after a day or two. Any thought on how to prevent this?

    • The clear film is likely just protein build up on the surface. It’s from the tank being very still (no current). You can just skim it off the top anytime it appears.

    • They do help filter the water and emit oxygen as well, but they don’t fully replace the function of a filter.

  8. I want to purchase a Betta with a 5 gallon tank, heater and a filter (and sand, decor). The water has to be 80 degrees for the Betta. Will the Marimo Moss Ball be okay in the 80 degrees water? Thank You

    • The marimo moss ball will be okay in that temperature. What I do, once a month or so, is place the ball in a plastic baggie or container and put it in the fridge for a couple days if it’s starting to fade in color.

  9. Do you see a problem with taking a large moss ball and breaking it into a number of small 1/2” balls, to be distributed around the bottom of the tank like a carpet ?

  10. I have a beta that recently started hiding under the smooth glad disks on the bottom of the tank. Might he be bored?

    • Hard to know from your comment alone, but betta like to hide at times. They can be increasingly lethargic or act peculiar if the water is too cold or dirty.

  11. Little shrimp (ours were cherry) in tanks with Moss Balls propagate the moss balls very quickly! We discovered this when the little shrimp ate bits of food on the balls, then when they travelled around to other parts of the tank, they took little pieces of algae and inadvertantly “planted” the algae on the substrate and aquarium wood. In a few months we had dozens of baby moss balls started – stuck to the log in clumps and rolling around on the floor of the tank! Their growth slowed down after they were initially established, but we also used to dose our tank with fertilizer as we had many, many plants in it.

    • It really depends on the size of each moss ball. They should complement the tank visually, and have room to move around. I personally keep 2-3 in my 5-gallon.

  12. Can I keep a keep a group of Marimo in my outdoor pond to help with the algae? I live near Salem Oregon.

  13. My betta is currently on a bettafix treatment for suspected fin rot. Is it ok to have the ball in their with the treated water?

  14. I just bought a moss ball, but I am hesitant to add it to my tank, because every time I rinse it off, some green residue comes off. Is this normal? Thank you!

    • Try submerging it in a bowl of water and gently squeeze it several times like a sponge. This should release any dirt and other residue that it’s holding onto.

  15. What’s a reliable source to buy from on Amazon? Specific vendor? I’m looking for smaller ones. Thanks!

  16. With my first betta that I got last year I managed to totally kill the Moss balls that I had, marimo or however you say they’re name. They became brown and mushy and eventually just disintegrated of course my poor betta fish also met with his demise. Matter of fact almost everything in that tank passed away and all I had was some Nerite snails which I’ll never have again, the marimo Moss balls and my one little betta. I’ve just purchased online from a reputable aquarium plant supplier a whole package of all different sizes. I have not put them in my two tanks that I have now one which has a very large mystery snail & my newest betta fish the other tank is a Fluval Spec V which only has two medium-sized mystery snails. I have the marimo balls in a 2 gallon Top Fin extra tank with nothing else in it but just the Moss balls because I’m very scared of putting them in with anything living, snails or fish. Am I being a little pessimistic or over cautious? I simply don’t want to introduced anything that might have a disease or fungus in with my newest betta because he’s all I have along with the three mystery snails and I happen to be very fond of all of them.

  17. Beware! Several “Betta Buddy Marimo Balls” have recently been found to have invasive Zebra mussels in them. You don’t want those in your tank nor in the outdoors!

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