Marimo Moss Ball Problems and Common Issues Guide

Your Marimo Moss Ball Problems Solved

Usually, Marimo Moss Balls do pretty well with only basic care needs, but problems and issues can still happen. They'll need sorting out to restore your plants to full health.

Normally, if you fix the cause of the issue and give your Marimo a little TLC for a few weeks, they will return to looking attractive and living happily in their displays.

Our guide will help you identify what's gone wrong and tell you how to fix the problem.

marimo moss balls growing in a dirty container with health issues

Although they can be known as algae balls, these ones are very dirty, not in good health and have problems that need addressing.

Don't forget to follow the basics with these plants. Check out my full Moss Ball care guide which tells you what they need to thrive in your care. It will save you a headache later on.

If you're reading this, then you probably already have a problem or two that needs to be sorted out. So let's get on with fixing this for you now.

What's wrong with my Marimo Moss Ball?

  1. Brown Sections
  2. White Sections
  3. The shade of green
  4. Floating
  5. Cracking
  6. Smelly
  7. Turning to Mush
  8. Condensation in the water vessel
  9. Stuck in vase
  10. Algae Taking over
  11. Dirty Moss Balls

Brown Sections

This covers small brown patches, brown spots, or large areas becoming brown. It's one of the more common issues owners come across and can have several causes.

Brown bits on a marimo

A cooler water temperature can play a big part in how healthy your plant is. Cold water is good, warm water should be avoided where possible.


It can be tricky to know exactly what's causing the issue, but it will be one of the following. Once you've established the cause, check out the "turning to mush" issue, which explains how you can fix the brown bits if they're quite extensive.

If there is just a little brown as shown in the photo above, then just cut it out and your plant should recover just fine.

  • Too much Sun.
    Marimo do not like full sun falling on them. Keep it out of direct light. If the brown bits appear where the sun rays are hitting, this is a good indication of the cause.
  • Too little sun.
    When the Moss Balls never get moved, or they're grown in very dark areas, any "sides" hidden from all light sources can die and go brown. Rotate or switch up the balls every few weeks to ensure all parts receive enough light.
  • Temperatures are too warm.
    Warm temperatures are another no no. If the temperature gets too hot, parts of your Marimo will start to die.
  • Dirty and unwashed.
    If you never wash your Moss Balls, then eventually, the dirt will allow unwanted Algae to take over, or harmful bacteria can start growing on it that will destroy the plant.

White Sections

This can look like a type of bleaching and look very strange. It's not overly common but there are a few things that can do this.


  • Direct Sun.
    Full sun can quickly bleach the green your Marimo. You'll know right away if this is the cause by establishing if sunlight is hitting the spots that have gone white.
  • Too little light.
    If most of the plant gets the right amount of light, but some areas are in total darkness. Perhaps the bottom is pressed up tight against the floor or an object in the growing container. Much like you might rotate an houseplant to stop it growing lopsided, the same principle applies here to fix it: keep rotating everything every few weeks as a minimum.
  • Too much salt in the water.
    In some cases you can give your Moss Balls a boost by putting a little salt into the water (I'll explain more about this later on), but if you give too much, it can cause parts to turn white.


The Color of Green

"How do I know if my moss ball is healthy?" This is a popular question, and it can often be answered by giving it a smell (yes really!), feeling it in your hands and how it looks. All three can indicate and guide you on how healthy your Marimo is.

The Green Colors

Generally speaking, all you need to worry about is if your plants are green. Minor differences in the shade of green is usually acceptable and not something that needs fixing.

  • Dark Green.
    Marimo growing in their natural habitats are usually a dark emerald green. They tend to have more significant concentrations of chloroplasts and chlorophyll to maximize the limited amount of light they receive at the bottom of lakes or rivers.
  • Light Green.
    Moss balls exposed to reasonably high light levels tend to have lighter green than those in darker spots. Generally, the plant needs less chlorophyll to do the same job, so as the concentration of this compound reduces, it can appear as a brighter green.
  • Not Green at All.
    Black spots, brown bits, white sections or looking discolored generally indicate issues. If these off bits are quite limited, you can remove them with a pair of scissors. Provide the proper care from now on, and the right color of green should return.


Is it OK for my Moss Ball to float? Another super popular question we get asked. Some people's Marimo go up and down in their fish tank or container several times a day, other people's sit on the bottom pretty much constantly.

marimo floats on top of the water

These aquatic plants can move around their home quite a bit with the help of an air bubble or two. The good news is that it's not a sign of health problems in most cases.


These are the reasons why your Marimo Balls could be floating.

  • You've just washed them.
    When you wash your Moss Balls (and you should, as it prevents them from getting dirty) it can introduce air into parts of the plants. When you pop them back into water, they can float for a little while. The air will work its way out of the plant in a day or less, and it should sink naturally.
  • Photosynthesis.
    During the day, rapid and intense photosynthesis could take place if they're getting quite a bit of light. This will produce an excessive amount of air bubbles that will cause floating. As the light levels decrease, the floating should stop.
  • Respiration.
    Plants often respire at night and this chemical process can again trigger floating. It's natural and nothing to worry about.


Question: "Why is my Marimo moss ball falling apart?"

Answer: "It's breaking to bits because it's 'Cracking'".

Cracking or splitting is what owners of Marimo call it when the spherical shape starts to open up. Bits might float away from the main plant or they stay attached but it becomes flat or changes to an odd shape, as you can see below.

Moss ball breaking apart and no longer round

Natural water currents help keep Moss Balls nice and round, but when grown in water that doesn't move it can lose the rounded shape.


  • Sometimes it's normal for indoor Marimos.
    Their native habitat is very different to what we provide indoors. The round shape is usually maintained naturally by river and lake currents, indoors we need to encourage them to stay rolled up. If we stop doing this, then cracking can occur.
  • Damage.
    The balls are held together with tiny filaments that grow and knit together to hold their shape. Rough handling either by the original growers or you can cause small tears and damage letting the plants split apart. Aquarium plants can be damaged by the aquatic life that shares the tank with them, like curious fish.
  • Incorrect Care.
    Prolonged incorrect care can weaken your plants and making internal damage more likely. If you want to learn how to care for Marimo Moss Balls, follow our care guide.

How to Fix Cracking

Fixing the problem is actually.... simple. Even if it seems a little strange to see in practice, it really does work.

The first thing to try is to wash and clean the affected plant and then roll it back into the ball shape (not sure how to do this? Read here).

Sometimes this is enough, and the problem is fixed, but if the cracking is quite extensive or it's not "holding" together after rolling, you need to move on to the next step.

Moss ball tired up with green thread to hold it together

Tying everything together like this is often a good idea. It effectively restores the circular shape and in time, new growth will grow over the binding and hide it.

If you can't get the ball shape to stick, then you tie it together with some fine cotton or fishing wire (nothing containing metal, or it could rust and cause problems in the future). Tie it around and around multiple times, like you can see in the photo above.

The cotton will keep things together. Eventually the Marimo will grow over this cotton and you won't know it's there. Some owners remove it after 6 months, but in reality, this can be tricky and could damage it again. I personally leave it in place.


How do I know if my moss ball is dying? Give it a sniff! A healthy Marimo has a faint smell of grass or generally "green" or mossy scent. It shouldn't be unpleasant. If it smells rotten or has an ammonia scent, then there is a problem.


Firstly check what's actually smelling bad. Is it the jar it's in, the water or the Marimo itself? The first stage is to clean everything, the jar, including any gravel or stones you have in there. The water should be changed and you need to wash your Marimo.

If all goes well, then that could be the problem solved. If the plant is falling apart in your hands or looking ill, scroll to the next issue below.

These are the things that will cause your plants to smell.

  • The water hasn't been changed in a long time.
    You need to change the water your plants are growing in every couple of weeks. If you leave it too long, nasties can start to take over and turn the water bad.
  • Heat damage.
    Excessive heat will speed up the microbiological activity within the growing container. It will also damage your plant and parts of it will die off and start to rot. They want a colder temperature, even in the hotter months of the year.
  • Too much light / not enough.
    As per the previous point, too much light or too little can damage your Marimo's ability to generate the right amount of energy from photosynthesis. If this happens, parts of the plant will die, creating nasty smells after a while.

Turning to Mush

A healthy Moss Ball should be reasonably firm when it's squeezed. Think of it like a mini tennis ball. Initially, it gives, but as you compact it in your hand, it gets firmer. When you let go, it should gently push back to its original shape.

If it's turning to mush or falling apart in your hands then it's in a pretty bad way.


Most of the problems mentioned on this page can lead to this "mush" if not addressed and resolved when they appear.

Can anything be done?

If the Moss Ball totally falls apart and is obviously dead then, it sounds like a lost cause. But if some bits are firm, or just minor repairs are needed then here's what you can do.

  • Clean and Salvage.
    First of all, you need to work out what you have. Clean and wash it gently, removing any black, brown or dead bits. Once you have a mass of green left, roll it into a ball shape using your hands. If it doesn't hold together, follow the cracking tips above.
  • Put them in the Fridge.
    This might sound mad but put them into a jar or container, fill with cool clean water and put this into the fridge for a day or two (no longer than this, but you can repeat the process a week later if you see positive results). The cold fridge gives your Marimo a huge boost as this is what they're used to in their natural habitat and can stimulate new growth and bring back some of the color.
  • Add Aquarium Salt (optional)
    You can add a very small amount of Aquarium Salt to the water your plants are growing in. Please do not overdo it. Do not use table salt or sea salt. This can contain harmful preservatives or additives that could finish your Marimo off for good.

    I don't recommend growing them in salty water for long periods, but a week or so is fine. At the next water change just use your normal type of cold water, for example, regular tap water.

Condensation in the water vessel

You may remember from your School science lessons that water will typically evaporate and turn into water vapor. You can't normally "see" this, but sometimes when you're growing Marimo you can.

The vessel or bowl can look cloudy, hazy or has water droplets on the sides of the glass container.

condensation on a glass beaker container

Condensation isn't really a problem for your plants, but it can take away from the "look" and aesthetic.


Some or all of the following cause condensation within the home of Moss Balls.

  • Sealed Container.
    If the vase or jar is sealed at the top then the water vapor can't escape. This means it will eventually settle on the coolest part of the container and turn back into water. You can prevent it by taking the lid off the top to provide ventilation.
  • Too Hot.
    Increased warm temperatures will speed up the evaporation rate and the amount of water vapor. Moss Balls don't like it too warm, so if you're seeing a lot of condensation, it could be a symptom that the temperature may be too hot.
  • Too much Light.
    Similarly, too much light, usually direct sunlight, can cause rapid heating of the water. Marimos aren't keen on too much light, so again, seeing condensation could be a warning sign about where you're trying to grow your plants. Don't forget; indirect light is plenty for them.

Stuck in vase

Because these plants grow soooo slowly, being stuck in a vase isn't that likely or common. But it does still happen!

A Marimo trapped in a glass jar

Smaller moss balls would escape from this opening, but this one has grown too big and needs some help.


This is simple. Your Marimo has got stuck because either the neck of the jar is too small, or the plant itself has grown.

  • Try and use growing jars that have wide openings.
    Small openings can add to the "ship in a bottle" look that people find attractive. But if you can't get your Moss Balls back out without damaging them, it's not going to work long-term, as they do need to come out for cleaning now and again.
  • The Marimo has grown. Or has it?
    They grow very slowly, often less than 5mm (0.2 in) a year. With this in mind, it's unlikely to get "stuck suddenly". What really happens is the ball shape starts to loosen over a few weeks and what might have been small and compact when it went in has expanded and opened out.
  • What's the Fix?
    There are three main ways to free your plants.
    Drain out the water, turn the jar over, and gently shake it out.
    2) You may be able to use your finger or a small tool like a pen to gently roll the ball out of the opening.
    3) Break the jar! (Do it carefully and be extra careful if the container is made of glass).

Algae Taking over

Marimo itself is a type of Algae called Aegagropila linnaei, but many other Algae species also exist. Some of these will grow on the Marimo directly and others will colonize on the container surface.

This can damage your Moss Balls in the long term and needs sorting. On top of this, algae growth can make your display itself look neglected and unattractive.

Moss Ball covered in Algae

"Bad" Algae can appear as a greenish, redish or brownish film or fuzzy buildup. It can grow on the Moss Balls directly or on any stones or gravel in the jar or even on the glass itself.


You can remove most of this Algae by cleaning the moss balls (see the next issue below), and the actual containers.

  • Too much light.
    Excessive light levels are not only bad for your Marimo in general, but it can cause explosive growth for "bad" Algae, allowing it to quickly colonise and spread. They only need indirect sunlight or even low light. Anything more is often problematic.
  • Too many nutrients.
    If you're feeding your Moss Balls, you're also potentially providing a nutrient source for other types of Algae. They really don't need that much feeding, so cut back on the fertilizer.
  • Too much time between water changes.
    The real problem is time. Even with the correct light levels and if you don't provide any feed, Algae will still start to grow in time. You can drastically reduce this setting in by changing the water frequently (at least every couple of weeks), and then giving the growing container a good scrub and clean every few months.

Dirty Moss Balls

Over time, like any houseplant, Marimo will shed cells and parts of itself. This is called detritus and if left to accumulate, can make your Moss Balls dirty and eventually unhealthy and sick.


  • Natural growing.
    As mentioned above, some degree of dirt is totally normal. It's important to wash and clean your Marimo regularly to prevent this buildup from becoming damaging. I give mine a good wash and roll them back into shape at least once a month.
  • Other organisms.
    In the previous problem I talked about Algae taking over, which will create its own waste. This would also apply to anything else that is living in the water with your Marimo. Wash your plants and change the water frequently, which will help keep things clean.
  • Not cleaning and washing.
    If you never wash your Marimo, dirt buildup will accumulate massively and this can discolor the water, make it smell and eventually has the potential to turn it into mush. Keep the water conditions healthy and clean for the best long-term results. You do this by running your Moss Ball under a tap, then gently squeezing it. Repeat until the water coming out is clean.

About the Author

Tom Knight

Tom Knight

Over the last 20 years, Tom has successfully owned hundreds of houseplants and is always happy to share knowledge and lend his horticulture skills to those in need. He is the main content writer for the .

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