Marimo Moss Balls For Betta Fish – Benefits, Care, & More

    Marimo moss balls for betta fish

    Marimo moss balls are eye-catching aquatic plants that are more popular than ever. What could be better than a living green pillow for your betta fish tank! But how difficult are moss balls to keep – and can they live in a betta fish tank?

    Marimo moss balls and betta fish can live together in the same tank. The water should be kept a little cooler since moss balls don’t do well with a lot of heat. They also absorb ammonia as they grow and release oxygen into the water.

    What Are Marimo Moss Balls, Anyway?

    Marimo moss ball
    Marimo Moss Ball (Aegagropila linnaei)

    Marimo moss balls go by quite a few common names. Including Cladophora balls, lake ball, or just moss balls. Most of these are inaccurate since moss balls are not made of moss at all!

    Marimo moss balls are a rare form of of cladophora algae growth (Aegagropila linnaei). Usually the green algae grows in a hair-like filamentous form, similar to algae you might find in any other pond or aquarium. It also attaches to rocks and driftwood.

    But the ball form is peculiar to cold, alpine lakes in Northern Europe and Japan. Here, the algae takes on a third form: that of moss balls. It rolls along the bottom, following gentle lake currents.

    This allows it to spread farther and colonize new habitats. The crystal clear water surface of their habitat is also important. Water clarity ensures that even if a marimo ball ends up in the deep, it will still have enough light for photosynthesis.

    Marimo moss balls also live for a very long time. The balls and patches of algae grow at around 5mm (.2 in.) per year.

    A large patch can be up to 8 feet across, suggesting a life span of decades in optimal conditions! Even smaller moss balls represent several years of growth.

    Moss ball care is a great way to get started with aquarium plants! This video breaks down the material covered here in a visual format:

    YouTube player
    Scientific Name: Aegagropila linnaei
    Origin: Northern Europe & Japan
    Size: Up to 1 foot in diameter (ball growth form)
    Lifespan: Up to 200 years
    Water Chemistry:  PH 6.0-8.0
    Preferred Temperature: 40°F-72°F


    Do Bettas Like Marimo Moss Balls?

    Adding marimo moss balls to a betta fish tank is a good idea! Betta fish like any decorations, plants, or tank mates that add enrichment to their habitat.

    Marimo balls bounce along the bottom if there are any currents in your fish tank. Small fish and shrimp hang around and within them, encouraging the betta to investigate it. Marimo moss balls also provide a handy resting place.

    Betta fish will perch on the leaves of aquatic plants at times. Taking a moment for a breather before continuing their search for food. Marimo balls look like a huge green throw pillow; the perfect addition to a betta’s domain!

    Can Marimo Moss Balls And Betta Fish Live In The Same Tank?

    Betta moss ball benefits

    Marimo moss balls and betta fish will live together in harmony. Bettas don’t eat moss balls and moss balls improve the water quality for bettas and any other fish.

    How Do Betta Fish Benefit From Marimo Moss Balls?

    Betta fish do benefit when living alongside one or more marimo moss balls. For one, the algae consumes ammonia released by the fish. As well as nitrite and nitrate that is created by your beneficial bacteria. But ammonia is their favorite form of nitrogenous waste.

    Moss balls don’t process all of it; that’s what your beneficial bacteria and filter are for. But they do add to the total denitrifying ability of your betta’s tank.

    Bettas also breathe in some of the oxygen that the moss balls release during photosynthesis. Not so much that they depend on it, however. Betta fish have a labyrinth organ alongside of their gills. They actually breathe atmospheric air as well as water.

    Moss balls for betta fish tanks are more decorative than anything. They create a much more enriching environment for your betta. Male bettas will perch and play among them. And hunt for food on and underneath one!

    Do Betta Fish Eat Marimo Moss Balls?

    Marimo moss balls are a soft, defenseless type of algae. Are they in any danger of being eaten by your betta fish?

    Fortunately, the answer is no. Bettas are carnivorous fish by nature, not herbivores or omnivores. Small insect larvae, shrimp, fish fry, and other moving prey are their preferred diet.

    A marimo moss ball is a good place to hunt. But they won’t graze off of it. If you see what looks like grazing, the betta fish is likely plucking bits of uneaten food off of the moss ball.

    Or it’s biting and tasting the marimo moss ball out of curiosity. Since fish don’t have hands like we do, they explore the world using their mouths!

    How Do Marimo Moss Balls Benefit From Betta Fish?

    It’s clear that bettas love marimo moss balls. But the moss balls also benefit from living alongside a betta fish. Like any aquatic algae, moss balls need nutrients to grow. The small amounts of ammonia released by a single betta fish are the perfect fertilizer for them.

    I recommend keeping moss balls in a single betta fish tank, rather than a crowded community tank. The lower nutrient levels are ideal for them.

    A solitary betta offers just enough nutrients for good moss ball growth. Without the algae ball becoming overwhelmed by nuisance algae that will grow if the water is too rich.

    Betta fish also breathe like all animals. They inhale oxygen, one of the many marimo moss ball benefits released. And exhale carbon dioxide. This CO2 is then taken up by the moss balls and released again as oxygen into the betta tank.

    A moss ball is not as good as an air stone for oxygenation but it does help. Betta fish also breathe atmospheric air so the moss ball isn’t keeping the betta alive on its own.

    Highly oxygenated water does promote clean conditions and helps aerobic bacteria thrive. Oxygenated water is also less likely to smell bad!

    How To Care For Marimo Moss Balls In A Betta Fish Tank

    Marimo moss ball care is not very difficult. They are also very long-lived. But strangely enough, the vast majority of them die in the care of fish tank hobbyists. Why might that be?

    There are three things that marimo moss balls need that the average fish tank might lack:

    • Cool tank water
    • Water flow
    • Low nutrient levels

    Cold Tank Water

    Here is a big reason why tropical fish tank keepers struggle to keep a marimo moss ball alive. These are not tropical plants; they come from cold conditions high in the mountains.

    Low temperatures are best for a moss ball. Yet a betta fish tank should be kept warm (72-82°F). So how can we keep betta fish and marimo moss balls together?

    Keep the temperature of your betta tank as close to the low end of this range as possible. Marimo moss balls would prefer it even cooler but we still want some warmth for our tropical betta fish.

    You may see some signs of stress in your moss ball. But not nearly as much as when kept in very hot conditions. You will also have an easier time treating these symptoms of heat stress.

    Water Flow

    Marimo moss balls also need a gentle current to keep them in a healthy ball shape. If moss balls are allowed to just sit in one place, the top section will get too much light. While the bottom won’t get enough light, causing it to die off.

    The ball will start to form a loose pancake. Or it may disintegrate entirely. If this happens to your marimo moss balls, you can take the pieces and try tying them to rocks or driftwood.

    If the conditions are otherwise healthy for them, the cladophora algae will attach itself over time. Forming a patch of fuzzy greenery that’s just as beautiful!

    There are a few ways to generate a slow current for your marimo moss ball. One is to use a bubble wall or other aeration device in your betta tanks.

    The flow of air bubbles does more than oxygenate the water. It also creates a circulation current for the marimo balls.

    You can use the outflow of a filter or powerhead to create water circulation as well. The only downside is that the moss ball may end up getting stuck in one corner of the tank, requiring you to move it to a new section over time. This only needs to be done every week or so; the section being shaded won’t die right away!

    Low Nutrient Levels

    This last point might surprise you the most. After all, marimo moss balls are like any other aquatic plants. They feed on ammonia, nitrite, nitrate, phosphates, and other nutrients.

    The average fish tank has loads of these nutrients. They come from fish waste and leftover food that breaks down over time.

    The issue here is the slow, slow growth rate of marimo moss balls. They are optimized for low energy, low nutrient conditions. Too many nutrients interferes with their growth.

    It also gives opportunistic algae species the ability to grow right on top of a marimo moss ball, competing for light and nutrients. You want pristine water quality when keeping marimo moss balls.

    Betta fish are some of the hardiest fish around. But many fish keepers don’t keep up with water maintenance as well as they should.

    A betta will tolerate moderate levels of pollutants. But moss balls won’t do well. They want the same pristine conditions as their alpine lake habitat.

    How Many Moss Balls Can You Keep With Bettas?

    How many moss balls with betta fish

    When you buy marimo moss balls, choose enough to coat up to 50% of the bottom but no more than that. Too many moss balls will make aquarium maintenance harder.

    It will be easy for leftover food to fall between and under the moss balls. This will contribute to a rise in ammonia, nitrite, and nitrate levels. Moss balls actually need even cleaner conditions than betta fish do.

    You can also keep just a few, or even one moss ball, if you wish. Fewer moss balls means more room for them to roll and circulate around the tank. Plus you can add other hardy plants to create a lush green jungle in your fish tanks!

    How To Choose A Marimo Moss Ball

    Moss balls good for your betta tank will have a vibrant dark forest green coloration. Avoid moss balls that look overly pale or brown. The yellower they become, the less healthy and closer to death the ball is.

    A few tiny brown spots is no cause for concern as these will recover fast. But larger patches of brown should be avoided; the entire ball is at risk of rotting away.

    Select a ball with a nice, round shape. Balls that are too oblong may be falling apart from within. Be sure to inspect your new marimo moss balls for signs of bad algae, snail eggs, and other hitchhikers. The feel of the ball should be firm, with a solid core.

    Don’t buy moss balls for betta fish that feel too squishy. That is a sign that the interior may be rotting. Moss balls sometimes die from the inside out.

    They will look healthy and green outside, but the interior rot progresses until it dies. Compare a few of them in the store to get a feel for their natural consistency.

    Many pet stores keep moss balls alongside snails in planted tanks. Snails are good at keeping moss balls clean. But once you have snails, getting rid of them is difficult to do.

    It only takes one snail or batch of snail eggs to cause a never-ending battle in your new tank. So prevent the battle from ever happening by choosing moss balls from snail-free fish tanks.

    Symptoms Of Sick Marimo Moss Balls (And How to Treat Them)

    A marimo moss ball rarely gets sick. But they do have issues that arise when kept improperly.

    Brown Patches On Marimo Moss Balls

    One common symptom of sick moss are patches of brown color. These indicate that the moss ball is starting to die off in places.

    Start by examining the placement of the brown patches. Is there a single large patch or several scattered across the moss ball? A single large patch suggests damage from bruising or grazing.

    If the patch is directly under the moss ball, it’s likely that this portion is dying from a lack of light. That means the moss ball is not getting enough current to keep it rotating well.

    Direct sunlight can also harm a marimo moss ball if it is exposed daily. These live plants prefer moderate to low light since they don’t grow very fast.

    But what about brown spots all over the moss ball? This suggests that the ball is being stressed by an environmental factor. Heat stress is the most common reason, especially in tanks for Siamese fighting fish.

    A moss ball won’t die immediately if kept warm all of the time. But the heat will slow its growth until spots die.


    Since they need cold, the best way to regenerate a stressed moss ball is to put it in the refrigerator for a day or two! The cold gives it a chance to recover. When removed, the ball often looks much more vibrant. But it may take time for the brown spots to fade.

    Opportunistic Algae Growth

    Marimo moss balls grow so slowly that sometimes other algae will try and attach to them. Stringy staghorn algae, black beard algae, fuzzy green hair algae…All of it will colonize a moss ball if given the chance.

    Since a seaweed ball is a living thing, it has ways of keeping other algae from taking hold. But a moss ball that’s stressed or weakened may lose this battle.

    Opportunistic algae growth is a sign that the betta fish’s tank is has too much light, poor water quality, or both. Problem algae loves both of these conditions.


    That means it’s time to start doing some water tests. You likely need to do some water changes to bring nitrate, ammonia, phosphorus, and other parameters back down again.

    Can Illnesses Spread Between A Marimo Moss Ball And A Betta Fish?

    Marimo moss balls are plants and betta fish are animals. They can’t share diseases since disease-causing organisms are very specific to their hosts.

    At best, a disease will spread between different members of the same kingdom, such as different kinds of animals. But infectious agents that can cause illness in both animal and plants are very, very rare. Even diseases that cross the boundaries between closely related species are rare.

    What can happen is that your marimo moss balls spread fish diseases from one tank to another. What if the tank you have a moss ball in has an ich, anchor worms, or velvet infection?

    Some of the free-swimming larvae may be living inside of the moss ball. Moving a moss ball to a new tank can spread the disease there. So don’t be too quick to change moss balls around between fish tanks. Any pathogens that live in one fish tank may hitch a ride over to yours!

    Cleaning A Marimo Moss Ball

    Marimo moss balls do tend to capture debris over time. Bits of fallen food will stick to them. Detritus, betta fish poop, and other kinds of algae will build up on their round shape.

    This happens most often in aquarium water that has little to no current. In nature, a moss ball rolls across the bottom, pushed by circulating lake currents. Little debris forms on them, as a result.

    Debris also blocks light, making it harder for a moss ball to grow. Gentle cleaning may be required about a week or two after buying one.

    Aquarium Snails As Moss Ball Cleaners

    One way to clean moss balls is to allow your freshwater inhabitants to do it for you. Betta fish aren’t good cleaners but aquarium snails are. Smaller species like bladder and ramshorn snails do the best job.

    Apple and mystery snails love eating unwanted algae and debris as well. But they grow so big that the moss balls will roll over when they try to climb on top of them!

    The main downside to using aquarium snails as cleaner is that they tend to reproduce so much they grow out of control. Since betta fish don’t eat snails, you may have to control them by hand.

    Fish That Clean Marimo Moss Balls

    Many smaller algae eating fish will also keep your moss balls free of algae and debris. My favorite is the dwarf otocinclus catfish (Otocinclus vittatus). They enjoy the same conditions that betta fish do.

    Dwarf otos are peaceful, growing no larger than 1 inch in length. And they won’t eat the moss ball algae, feeding only on opportunistic algae that grows on top of them.

    Plecostomus are too large and unruly. The larger they get, the more likely they are to outright eat the marimo moss balls.

    Cleaning A Moss Ball Yourself

    You can also hand-clean marimo moss balls. All that is required is to gently squeeze them once per week. You can place them in a small cup of tank water before doing so. Debris caught on the surface and within will come gushing forth.

    I also recommend giving your moss balls a cold temperature bath after squeezing out debris. Even just a few hours of cold will do them a lot of good. But if you can, 24 to 48 hours of refrigerator time will perk moss balls up substantially.

    It is also good to carefully roll your moss balls by hand inside of the tank once per week. This maintains their spherical shape. It also ensures that all sides of the ball get adequate light exposure.

    Without occasional maintenance, marimo moss balls are prone to browning on the bottoms. If not rolled, they will lose their shape and start to rot. Eventually disintegrating entirely.


    Marimo moss balls do well alongside betta fish. They are great for removing waste in small amounts. The moss adds extra green growth to your aquarium without the difficulties of other live plant species. And they give your betta an even more enriching environment to live in!

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