Marimo Moss Balls for Betta Fish: Care & Benefits (Updated)

marimo moss ball
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Last Updated: September 4, 2023 by Flora Gibbins

Even though Betta fish, or Siamese fighting fish, won’t chew on live plants, it can be difficult to find plants that won’t overgrow a small aquarium.

If you are keeping a betta fish without any other tankmate, it may not even produce enough bioload to support smaller-sized plants. In a smaller tank setting, this can spell disaster because of the need for fertilizer.

Plus, most aquarium plants don’t provide much mental stimulation for your bettas.

Fortunately, moss balls for betta fish tanks offer the perfect solution to multiple small aquarium challenges.


At first glance, you might think a moss ball for bettas is bad because they are made up of algae. Even if you’ve only had a fish tank in operation for a few months, then you know how difficult it can be to control algae growth.

Marimo Moss Ball Guide

Unlike the kind of algae that coats the walls of the aquarium, the algae in moss balls stick to themselves to create clumps.

As such, a Marimo moss ball for betta fish will never overtake your tank or pose a hazard to betta fish and other aquatic creatures.

They are also very easy to care for. This form of algae, originating from the waters of Japan, Iceland, and Scotland is ideal for betta tanks regardless of size or age.

Marimo Moss Balls Make Good Betta Fish Toys

The sad reality is finding suitable tankmates for male Veiltail betta fish is complicated. 

There are very few fish that won’t destroy bettas because betta fish start off with aggressive posturing to other fish.

Once the other fish decide to put male bettas in their place, the betta fish has neither the strength nor the speed to deal with the problem. In most cases, this will also kill the betta. 

On the other side of the equation, bettas are incredibly intelligent creatures that need mental stimulation.

Just the same, not all bettas are eager to interact with humans or want to learn tricks via r2 fish trainers.

While bettas aren’t especially anti-social, they don’t school or shoal like other community fish. Even if you do find suitable fish, the betta usually won’t interact much with them. 

They are somewhat similar to angelfish, cichlids, and fantails in the sense that they will move things around the fish tank to suit themselves.

Unlike other species, however, bettas are much more inclined to move things around purely for the sake of amusement. 

What they lack in terms of the need for play-based social stimulation, they more than make up for the need for betta fish toys.

This is why DIY moss balls make ideal betta fish toys.

Larger balls will stay on the bottom of the fish tank, where bettas can roll them along as much as they please. Even if you have smaller bettas, you can easily adjust the size of this fish toy to suit its needs.

Smaller moss balls will float around in the tank, and make for the best toys at all levels of the tank. 

Adding marimo moss balls to your tank.

Unlike the Zoo Med betta log toy or even a leaf hammock, you never need to worry about bettas scraping into sharp surfaces left over from the plastic molding process.

In fact, if you decide to buy Zoo Med floating betta logs or other log accessories, you can attach the moss balls to areas of the betta log that might be dangerous to the fish.

This won’t work out as well for a leaf hammock because there may be too much weight for the suction cup to handle. If you find the leaf hammock falls off the side of the tank, you can try adding a bigger suction cup.

3 Ways Moss Balls Keep the Tank Clean

When I first started aquarium keeping, I was very careful about getting rid of even the smallest amounts of algae in my tanks. 

Then, I went through a phase where I let it build up some, thinking that there are definite benefits to these plants being in the tank.

Over time, I have evolved to more of a balanced approach. I do allow some algae in my tanks, but not enough that a die-off would kill everything in the tank.

A DIY Marimo moss ball for betta offers a very easy to control form of algae that can help keep the best fish tank you have clean without taking up room in critical swim areas. 

Here are 3 ways a betta moss ball can keep an aquarium clean:

1. Moss balls require nitrates to live

Good bacteria convert fish waste into nitrates. Once that is done, the recycling process must be completed by some kind of plant. In this case, moss balls do the job effectively.

2. A betta moss ball takes in carbon dioxide and emits oxygen

Tropical fish and other animal-based creatures in the tank constantly exhale carbon dioxide. 

Without plants or algae, the only source of oxygen in the tank is what gets through the water surface as a result of filtration disruption. Since your filter is likely to be set at very low levels in a male betta’s tank, oxygenation from plants, or in this case, moss balls, is essential. 

3. A betta fish moss ball can compete with other forms of algae for nutrients

As much as I love keeping live plants in a tank, they simply don’t grow as fast as algae. In fact, I’ve often had to clean algae off the leaves of plants just to keep the plants from suffocating.

Moss balls, on the other hand, consume a good bit of nutrients within their tightly locked matrices. As a result, they are one of the few plant-based aquarium inhabitants that can keep up with more common forms of algae. 

Position moss balls

Providing a Home for Beneficial Bacteria

Good bacteria love to collect in places with plenty of cavities and recesses. When those cavities also have plenty of water flowing through them, it’s even better.

In this respect, moss balls are living filter floss or similar media. As long as you don’t deprive them of light, they will provide a natural place for good bacteria to live. 

If you are looking to explore natural, renewable self-cleaning tank options, Marimo moss balls offer a distinct advantage over filter floss and ceramic disks. As long as the moss ball is alive, you will never need to replace it. So don’t let this aquatic green die!

As an added bonus, if you decide to start up a new aquarium, you can simply break off a piece of an existing ball and add it to the new tank. 

This will jump-start the nitrification process in the new tank better than using other types of bacteria additives. 

Work Perfectly in Smaller Tanks

Many times, I’ve visited with friends and family, only to see veiltail bettas struggling to reach the surface of tanks that hold more than 2 gallons of water.

Each time, these well-meaning aquarium keepers explain they were told these fish need at least 5 gallons of water. 

While a plakat or smaller tailed betta may do a little better in a big tank, it is a death sentence for veil tails. 

Probably the saddest thing is when I get a call or text from these very same people saying they don’t understand why their betta died. Or, they ask how I knew this is what would happen.

With close to 30 years of aquarium-keeping experience, rest assured I’ve tried more than once to put veiltail bettas in larger tanks. The result was always the same. A dead fish within about a week.

As a case in point, have a look at the following video.  This betta is clearly showing signs of serious distress.  

He is unable to swim in the bottom region of the tank.  His color is very pale, in particular under his mouth and gill region.

In addition, his need to put his nose straight up to reach the top of the tank is a clear indicator the water is too deep. 

I would be very surprised if this fish lived much longer.

Just because there are limits to tank size for bettas, that doesn’t mean you should ignore exploring how to add live plants to the aquarium.

Sadly, just about every aquarium plant will grow too fast and overtake the swimming area too fast. 

Marimo moss balls are perfect because no matter how fast they grow, they are easy to control and won’t obstruct swimming areas.

Marimo moss balls in aquarium.

Easy to Care For

Keeping a live plant in smaller tanks can be difficult to manage from several perspectives. One of these is the fact that a single fish can only produce so much waste.

Aponogetons, Anubias, java ferns, swords, and others can quickly run out of nitrates even in a tank with a larger number of fish. 

In fact, some of these aquatic plants routinely require additional fertilization or CO2 injection to live.

These things are dangerous and unsustainable in small tanks that most bettas are best suited for living in.

By contrast, Marimo Moss Balls don’t require any additional fertilizers and are very hardy. Even if they start to get yellow or brown, you can simply take a few out of the tank so there is less competition for nitrates.

You will also find that moss balls are much easier to trim and propagate than other live plants. While some plants will survive robust pruning, others won’t do well even if you remove 1 or 2 larger leaves.

There is very little guesswork involved in how much to prune from a moss ball. When in doubt, just divide it in half. Both halves will grow out again and do just fine.

4 Essentials to Caring for Marimo Moss Balls

Knowing the answer to the question “How to add moss ball to a betta tank?”  is very important.  

The answer to this question and also, “How to introduce moss ball to betta tank?” has everything to do with ensuring the moss balls have what they need to survive.

To enjoy healthy robust Marimo moss balls, there are 4 things you must keep in mind:

1. Proper lighting

As with other plants, moss balls also require the right amount of light over a specific period of time. Similar to common aquarium algae, moss balls do best with medium, indirect light.

If moss balls are exposed to excess light, they will turn brown. When this happens, you can try scraping off the brown surface to expose the bright green below. Next, be sure to put the moss ball in a spot with less lighting. 

When moss balls don’t get enough light, they will steadily become faded-looking and eventually turn yellow. If you see this, simply move the ball into a brighter area of the tank.

2. Proper temperature range

Contrary to popular belief, moss balls don’t do well in all water temperatures. Most people say moss balls will do best in temperatures from 72°F to 78°F. 

Personally, I’ve had no problems keeping them in temperatures as low as 70°. Moss balls originate in lower temperature waters, so they will do better on the lower end of the spectrum. 

3. Sufficient nitrates and carbon dioxide

As with any other plant, moss balls require a certain amount of nitrates and carbon dioxide. 

It isn’t enough for the nitrates and carbon dioxide to simply exist in the tank with them. Water carrying these nutrients must flow through the entire moss ball so that algae in the center of the ball can receive nourishment.

Before you conclude there isn’t enough nitrate or carbon dioxide in the tank, try dividing the moss ball into smaller pieces. If they continue to grow slowly, then you might want to remove some of the balls from the tank.

4. Proper Division

When I got my first moss ball, I was very hesitant to divide it for the first time. Nevertheless, this is one of the most important parts of Marimo moss ball care. 

If you are hesitant about dividing the ball, try leaving a larger piece and a smaller one. Then, you can observe the two and figure out how small you want to make the pieces at each division.

Mini marimo moss balls.

Frequently Asked Questions

1. Are moss balls good for betta fish?

How well moss balls work in a betta fish tank is closely tied to the question “what do moss balls do?

Marimo moss ball benefits go well beyond the joy of seeing a betta playing with a moss ball.  

Moss balls offer key play-based stimulation even as they help keep the tank clean.

2. Should I divide moss balls as they get bigger?

Yes. When moss balls get too big, the inner levels of the ball don’t get as much water flow and nutrients. This cuts back on their efficiency insofar as keeping the tank clean. 

 It also leads to a situation where the starved inner portions of the moss ball die off. Eventually, the rot in the inner can spread outward and kill off the entire moss ball.

Fortunately, dividing a moss ball is very easy. All you have to do is break a larger ball into 2 or more, smaller pieces and place them in different parts of the tank.

3. What do moss balls require to live?

Moss balls require water, light, carbon dioxide, and nitrates. They do not require fertilizer or CO2 supplementation. Even a single betta can provide enough carbon dioxide and waste for several moss balls. 

4. How do I know if my Marimo moss balls are dying?

In the beginning, the moss ball will not grow as quickly. You may also notice other kinds of algae building up on the surface since the ball itself isn’t taking in nutrients.

In the later stages, the moss ball will turn yellowish and then brown.

5. How do I clean moss balls?

Start off by removing the moss ball from the tank. 

Rinse it gently in clean aquarium water or another aquarium-safe conditioned water. Never use water straight from the tap because it may have chemicals in it harmful to the algae living within the ball.

Next, gently scrape off any debris remaining on the moss ball. Keep going until you reach a vibrant green surface all the way around the ball.

Finally, if it is getting too big, divide it into 2 or 3 pieces before placing back in the tank.

6. How do I use moss balls in a filter-free tank?

Male bettas are extremely sensitive about their bubble nests

Unfortunately, the job of filters and airstones requires the kind of disruption that easily damages these nests.

Marimo moss balls can provide oxygen directly from under the water as opposed to relying on oxygen from the air getting into it. 

If you are aiming to keep a male betta without a conventional filter, the moss ball can go a long way towards achieving this goal from an oxygen perspective. That’s a betta fact!

7. Can I use moss balls in a tannin-rich betta tank?

When I first started out in aquarium keeping, I never thought I would venture into tannin-rich or low pH tanks. 

Bettas, on the other hand, do exceptionally well in this darker-colored, acid-rich water. 

In fact, I’ve revived more than one sluggish betta by placing Catappa leaves in the tank. 

Moss balls can take a pH no lower than 6.0. Therefore, if you are planning to lower the pH of a betta tank using Cattapa leaves or other tannin sources, you will need to watch the pH carefully.

When you put betta fish and moss balls together, be sure to keep pH up adjusters on hand, and also some activated carbon to sequester the tannins. 


Marimo moss balls offer several advantages over live plants for a betta tank. Moss balls are easy to care for and require very little in the way of maintenance. 

They also offer a perfect alternative to other live plants that may take up too much space in a small tank.

Unlike other plants, they also provide a unique toy for curious bettas and other pet fish.


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