Guide to Marimo Moss Ball Care

Marimo moss balls are balls of algae that make good additions to unheated and tropical fish tanks. They don’t need extra nutrients or carbon dioxide when kept with aquatic pets. Occasional rolling, trimming, and cleaning will be done every so often. And they need to be chilled if they stay warm for too long in a tropical tank.

Marimo Moss Ball

What is a Marimo Moss Ball?

Marimo moss balls are a spherical form of cladophora algae. The word “marimo” is a Japanese term that translates to “algae ball”. Moss balls are found in cold, alpine lakes in Japan and Northern Europe.

They do grow flat on hard surfaces, like other types of algae. Patches of algae sometimes get caught up in the slow currents along the lake bottom. As they roll about they take on a spherical growth form.

Many circular plant and fungal growths have a center. But the Marimo does not. Each round shape is algae all the way through.

Aquarists sometimes worry about adding marimo moss balls to an aquarium. Since they are a kind of algae won’t they grow out of control and green every hard surface?

Marimo balls are not capable of spreading in your fish tank and growing like normal algae does. It remains in a compact ball form.

Marimo moss balls don’t grow fast, and they won’t spread to other parts of the tank. It can only grow in clumps and does not attach itself to other objects in a fish tank.

Marimo moss balls won’t attach themselves to decorations or other parts of the tank. But it is possible to glue the Marimo moss balls to decorations. Just know that this can cause long-term damage because they evolved to roll freely with water currents.

You can also create attractive “grassy” areas of the tank by gluing multiple Marimo balls to one area. Faux trees with them are also popular with aquascapers.

Even though Marimo ball algae is hardy, it is prone to rot under certain circumstances. Rot is the main killer of Marimos in aquariums, and it is caused by improper care or water parameters.


Why Do Marimo Moss Balls Cost So Much?

When you first go to buy a Marimo moss ball, you may find yourself surprised at the price. They are often $6-8 for just one Marimo moss ball, or $10 for three mini moss balls.

In the big picture, this isn’t really that much. But for this price, you could get multiple java ferns, multiple Anubias, or several large bunches of Brazilian waterweed.

So why does this algae cost so much when compared to common aquarium plants?

The primary reason for the price is the slow growth of this algae.

Java ferns and Anubias also have slow growth rates. But large production firms can speed up growth with fertilizers, high lighting, and ideal water parameters.

Fertilizers have little to no effect on the growth of a Marimo Moss ball. These moss algae balls grow one-half to one centimeter per year. It will take four or five years to grow them large enough to sell. Because they take so long to cultivate, wild harvesting is common.


Marimo Moss Ball Care

marimo moss ball
Piotr719 [CC BY-SA 3.0]

Marimo ball care is not advanced but they will die if you don’t meet their temperature and nutrient needs.

Water Parameters for Water Moss Balls

\Water temperature is the most important element to successful Marimo moss ball care. Most aquarists don’t know this but they grow only in cold water habitats.

In their mountainous home region water temperatures are cold. Glacial meltwater keeps the lakes fed, which is is pure, chilled, and free of high nutrients or minerals. Temperatures above 75℉ are stressful for them and your Marimo moss balls will stop growing. If the temperature remains high they will eventually die.

Marimo balls are more flexible when it comes to water pH. But they prefer neutral to slightly alkaline conditions (pH 7.0+).

As far as lighting goes, mossballs are not picky. Whether the lighting is low, medium or high, they will do well in a fish tank.  Keep Marimo balls in high light environments when there are other plants to compete with algae growth for nutrients. Even high lighting won’t force Marimo moss balls to grow faster.

Marimo Moss Ball Care Tips

While most plants can simply be planted, fertilized, and forgotten about, moss balls need more intensive care.

You should roll your Marimo at least once a week. You press it in your hand and roll it to keep a circular shape, or flip it every week in the aquarium.

In nature, moss balls roll around the bottom of alpine lakes as currents push them along. The continual rolling helps them keep their round shape and ensures all sides get access to light and nutrients. Since they are not rolling around in aquariums, they will begin to flatten out if left to sit.

The abnormal shape looks bad but is not an issue. There is another issue that may arise, however. The bottom part of a Marimo will rot if it is not rolled often enough.

Marimo balls need a little exposure to light to live but the bottom part is not being exposed to light at all if left to sit. If you wait too long to flip or roll your Marimo, you may find that the bottom part has begun to rot.

When the rot is not too bad and only some discoloration is visible, you can leave it on. The mossball should be able to recover.

If the rotten part has turned a deep or light gray, you should try to separate that section using sharp planting scissors before it rots. Then roll the live, green portion into a sphere, and place the algae ball elsewhere in the tank.

If there are no signs of recovery after a few days, toss out the rotten part to avoid an ammonia spike.

How to Clean Live Moss Ball

As they roll around, or as the water current brings particulates over to them, Moss balls tend to accumulate mulm and crud, similar to a sponge filter.

While a sponge filter cannot do anything with the mulm, Marimo Moss balls will use some of it. But they absorb more than they need and should be cleaned every few weeks.

To clean a moss ball, take it out of the tank and place it into a separate container of dechlorinated water.

Squeeze it multiple times in the water, and you should see mulm coming out of it. After squeezing it, you can reshape and place it back into the tank.

Note that after squeezing it, most of the water is also squeezed out of the Marimo.

This may cause it to float for several minutes to several days. As long as the marimo moss ball sinks again after 2-3 days it will be fine.

Reviving a Dying Marimo Moss Ball

Sometimes a moss ball in aquarium will appear sick for no reason.

Your water quality may be perfect for them, everything else in the tank is thriving, and your plants are growing fast. But the Marimo is just sitting in the corner turning brown or gray.

Even with frequent rolling, reshaping, cleaning, and good lighting, it seems to rot away.

Even though Marimo moss balls are able to survive most water temperatures, they will become sick in water temperatures over 70 to 75 degrees.

To fix this problem, take your Marimo out of the tank and place it in a jar or other container of tank water.

Next, place it in your fridge overnight. Take it out in the morning and place it in or near a window.

Leave it in a cooler area, or just room temperature, where it is able to receive direct sunlight. After just one or two days, there should be a visible increase in the health of your aquarium moss balls.


What Do Moss Balls Do?

Marimo moss balls are sold as “betta buddies”, “tank enhancers”, and “shrimp buddies”. But these algae balls are decorations. They grow slowly and they do not change much. Algae balls are decorative additions to any fish tank that isn’t too warm.

Algae balls will convert some nitrates into energy. But it will not be enough to make any difference on the overall nitrate levels. For purifying your tank water, fast growing species like floating plants do a better job.

Some betta fish seem to enjoy having a live moss bal around. They will rest on or near them, or even push them around the tank.

Shrimp enjoy these moss balls and will sit on them for hours. They picking at the mulm that gets collected as the ball rolls around the tank. For freshwater shrimp, these moss balls are a feast.

Marimo moss balls can also be used in the creation of “Bonsai trees” using driftwood:


Tank Mates

When it comes to tank mates, most fish and invertebrates are safe to keep with moss balls. Some fish will develop a taste for them, however.

For example, while a carnivorous fish like a betta fish won’t eat them, a massive herbivorous fish like a goldfish will devour one in a few minutes.

I recommend keeping at least one Marimo Moss ball with freshwater shrimp due to the amount of biofilm that grows on the moss ball. Much of a shrimp’s diet is biofilm, so having a constant source is beneficial to their growth.


Pros and Cons of Marimo Moss Balls

Here are a few common benefits and drawbacks of owning Marimo Moss Balls.

Benefits

Even though Moss Balls primarily act as a form of decoration, they have the benefits of normal decorations as well as other benefits that normal decorations lack.

Just like any other decoration, fish within a certain size limit are able to hide behind or among Moss balls, which will help them feel more secure.

They will also increase the overall beauty of the tank. You could even cut them up and glue them to various areas of the tank, creating “moss” walls, “grass”, and even “trees”.

If the bottom part of the Marimo doesn’t get any sunlight, it will rot. So occasional rolling is rquired.

Moss algae balls do use a small portion of the nitrates, ammonia, and nitrite available. While this is beneficial they aren’t a replacement for a filter or water changes.

Marimo balls also need to be cleaned or debris will accumulate in them, suffocating the algae But marimo care also makes normal tank maintenance easier.

They collect a great deal of mulm and then hold it until you can clean them. As a result, you spend less time spot cleaning your aquarium.

Marimo moss balls also promote the development of biofilm and microorganisms. While this may not impact a tank that only has large fish, it is beneficial to shrimp, fish fry, and small fish species.

Negatives

The main negatives that arise from a Marimo Moss ball are caused by improper care. They are large, dense balls of organic matter. If one were to rot and die, it could cause an ammonia and nitrite spike.

Ammonia and nitrite are leading killers of pet fish, and no fish is immune to them.

If you see signs of rot on yours, be sure that you are cleaning it every few weeks and rolling it once a week. Ensure that the water temperature is not too high. If you can’t identify a major cause, use the fridge method for a few days to try and revive your marimo moss ball.

You should also remove the rotted areas and place them in a cup or bowl by a window, which may help revive that part.


Signs that Your Marimo Moss Ball is Dying

Keep in mind that the natural lifespan of this algae ball is well be over 100 years. And due to their hardy nature, most can come back from significant damage. So if your moss ball looks weak, you have an excellent chance at saving it.

The earliest sign is discoloration. The moss ball won’t changing colors in a dramatic way. But if some areas start to become lighter green than others, there is a chance that your moss ball is dying.

If the Marimo begins to turn brown, yellow, or gray, it is a sure sign that your moss ball is dying. If this area is one that does not often see light, it is simply dying due to a lack of sunlight.

Marimo algae makes its own food through photosynthesis, which requires an input of light and nutrients (waste). If it is unable to get the light it needs to make food, part of it will begin to rot and die.

If this part was already receiving light, there is something wrong with the chemistry of your water that is causing the issue.

Even though they do not directly require fertilizer, they still need to be able to access certain minerals found in normal tap water.

Any tap water should be dechlorinated, as the chlorine can damage them and any other inhabitants you may have with them.

Try increasing the frequency and amount of water changes you are doing. Doing so removes water that has more depleted minerals and replaces it with fresher water.

Normal tap water has enough minerals for this algae to survive. But it must be changed weekly to ensure the live marimo moss ball is receiving the proper amount of minerals.


How to Propagate your Moss Ball

Propagation refers to breeding animals or plants, but the Marimo moss ball is capable of asexual reproduction.

While they will not reproduce on their own in an aquarium, it is possible for you to propagate them. All you have to do is divide them into one or more smaller pieces.

Roll the smaller pieces and try to keep them as compact as possible, and place them back into the same aquarium, or into separate ones.

Over time, these will all grow and develop into separate little spheres. While they will often grow lopsided at first, reshaping them multiple times will help them grow into perfect spheres.

Since they grow so slowly, the growth will be more noticeable in smaller Marimo Moss balls than larger ones.


Marimo Moss Ball Size

For most plants, the maximum size will determine what aquarium you need to place them in from the beginning. It takes just a few months for them to reach their maximum size.

Moss balls can be moved gradually to larger tanks, or separated into smaller ones if they grow too large.

They are capable of growing up to a foot in diameter, which is quite impressive for this rare algae.

Such a large size is not common in aquariums due to the amount of time it takes for them to grow this large. In aquariums, five or six inches is considered a large specimen.

They are sold for fish tanks between ½ and 2 inches in size. If you buy one of the larger ones, feel free to separate it into smaller ones for extra marimo moss balls.

Conclusion

Marimo moss balls are the most unusual aquatic plants you will find in the aquarium hobby. They are slow growing and a little sensitive. But they will live for a long time when their temperature and nutrient needs are met. Algae balls also add interest to aquariums with other cold-water aquarium pets like shrimp and fish.

FAQs

Do Marimo Moss Balls Need Food?

Marimo moss balls don’t grow very fast but they do need a little fertilizer to maintain proper health. A steady trickle of ammonia from your aquarium fish is all that these slow-growing algae balls require.

How Long Do Marimo Moss Balls Live?

When kept in cold water conditions with low nutrient levels, you can expect your Marimo moss ball to out live you. They can grow for over 200 years, making them valuable in Japan as symbols for good luck and longevity.

Is a Marimo Moss Ball a Pet?

If you consider a plant to be a pet then absolutely. But since they are plants and you don’t usually “pet” slimy balls of algae, it is better to consider Marimo moss balls to be decorative additions to an aquarium ecosystem.

Can Marimo Moss Balls Live in Tap Water?

Tap water won’t harm a Marimo moss ball for short term stays. But it has no nutrients at all for growth so your moss ball would eventually starve to death. They don’t need much nutrients but a little is still required for growth and maintenance.

How to Trim Moss Balls?

Use sharp planting scissors to trim moss balls. If one side is growing faster then that is a sign to flip the moss ball more often.

What Do Moss Balls Eat?

Marimo moss balls feed on small amounts of nitrogenous waste like ammonia. Along with leftover phosphates and other nutrients from fish waste. They don’t require fertilizing when kept with fish or shrimp.

Are Moss Balls Alive?

Yes, they are. Moss balls are living balls of green algae. They require light, nutrients, and clean water, like other plants.

BYA Editorial Staff
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3 thoughts on “Guide to Marimo Moss Ball Care”

  1. I have a question. About 3 weeks ago I moved my aquarium. It was getting indirect light now it is getting direct sunlight for maybe an hour a day. 3 days ago right after a water change I noticed my Moss ball floating during the day and sinking at night. It has done this consistently for the last 3 days . Now I see slight brown spots evenly spaced around the Moss ball. Is this because it’s getting too much light?

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  2. I have a marimo balls at home..and yes i give them a spa..as i call it once a week in the fridge…i noticed that one of then have this bump actually 2 bumps..so i gently remove the bump and roll them nicely and now i have these 2big and 2small ones..did i do okay when i remove the bumps? Not harming them ?

    Reply

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