Marimo Moss Ball Care Guide

  • By: SFUAA
  • Date: December 17, 2022
  • Time to read: 8 min.

Marimo moss ball care is easy, but there are still important steps to follow if you want your marimo to stay healthy and happy. From water temperature to lighting, we’ve got all the tips and tricks you need for keeping your marimo in top shape. 

Read on for everything you need to know about marimo moss ball care!

Marimo Moss Ball Care

Marimo Moss Balls are a unique and fascinating species of aquatic plant native to Japan. They are small, round green balls of algae that can grow slowly but can get to be quite large over time. Marimo Moss Balls make great additions to any aquarium, providing a unique and attractive decoration that helps to clean the water and provide oxygen for other aquatic life. 

Caring for Marimo Moss Balls is easy, and with a few simple steps, you can ensure that your Marimo Moss Balls remain healthy and vibrant for a long time.

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Photo 254103118 / Marimo © |

First, you will need to make sure that you have the right environment for your Marimo Moss Balls. They prefer tanks with low to medium indirect light, so make sure to keep them away from direct sunlight or any other harsh lighting. They also prefer temperatures between 68-80 degrees Fahrenheit, so use a thermometer to make sure that your tank is in this range.

Next, you should make sure that your Marimo Moss Balls are kept in an aquarium with clean, fresh water. Be sure to perform regular water changes and clean your tank as needed. You will also want to periodically squeeze the Marimo Moss Balls gently in fresh water. This helps remove any dirt or debris that may have built up on the surface of the moss balls.

Finally, you can give your Marimo Moss Balls an extra boost of care by putting them in the refrigerator overnight once or twice a month. This helps keep the temperature cooler which is beneficial for the moss balls.

Prepare the Tank

One of the first steps in preparing the tank for a Marimo Moss Ball is to make sure the water is of good quality. It is important to use treated or filtered water, as untreated water can contain harmful contaminants. 

It is also important to keep the water temperature cool, as warm water can be damaging to the moss ball. Additionally, make sure to check the pH levels of the water to ensure they are at an appropriate level for the moss ball. Anywhere between 6-8 pH should be fine.

Marimo can go in any sized aquarium, even down to a small vase or large glass of water. If you don’t have fish in the same tank as your marimo, however, you will want to use a light application of aquatic plant fertilizer, such as Easy Green from Aquarium Co-Op (not sponsored, I just think it is a good product).

Lighting and Temperature Requirements

Marimo prefer low to moderate light and cooler temperatures, as these are their natural habitats. They should not be exposed to direct sunlight, as this may cause them to burn. 

Instead, indirect sunlight at the brightest, down to your average aquarium light will provide the enough environment for your marimo. The water temperature should also be kept cooler – up to 80F but ideally 77F or below, as warm water is not ideal for marimo. 

With these simple lighting and temperature requirements met, your marimo moss balls will thrive for years to come.

Fertilizer and Water Quality

Fertilizing and maintaining optimal water quality are two of the most important aspects of caring for your Marimo moss ball. Fertilizer is needed to provide nutrients for your moss ball and ensure it stays healthy. Water quality must also be monitored, as poor quality can cause algae blooms and even kill your Marimo moss ball. Here’s what you need to know about fertilizing and maintaining water quality for your Marimo moss ball.


Marimo don’t really require fertilizer if you have enough fish in your aquarium, as the waste from your fish and excess food you give them should provide enough nutrients for slow growing aquatic plants like marimo. 

If you don’t have many (or any) fish in your aquarium, a very light application of a fertilizer specifically for aquariums can help provide your marimo the nutrients it needs. I would start with 25% of whatever the instructions on the fertilizer you get say to apply if you don’t have other aquatic plants. Marimo are not heavy feeders, so the rest will go to feeding algae in your aquarium.

Water Quality: It’s important to monitor your tank’s water quality to ensure your Marimo moss ball stays healthy. Test the pH levels, ammonia, nitrates, nitrites and other parameters on a regular basis. Keep the pH between 6-8.

By following these tips, you can ensure that your Marimo moss ball stays healthy and vibrant for years to come!

Propagating of Marimo Moss Balls

Propagating Marimo Moss Balls is a simple and easy process that can bring joy to any home or aquarium. Marimo moss balls are a type of algae that grow in ball-shaped clusters in areas with low to moderate light. When cared for properly, these moss balls can grow quite large, up to 5 inches in diameter for a marimo around 25 years old. They are relatively easy to care for and propagate, making them a great addition to any home.

To propagate Marimo Moss Balls, first find a healthy specimen and gently squeeze out the excess water. Then, use a sharp knife or scissors and cut it in half. You can then cut each half into two or more pieces, depending on the size of the original ball. Place the pieces in a new container with fresh water and place in low to moderate light.

Marimo Moss Balls can be propagated in other ways as well. You can separate the individual strands of algae from the larger ball to create smaller moss balls. Or, if you have multiple Marimo Moss Balls, you can put them together in a larger container and they will join together to form a larger ball.

When propagating Marimo Moss Balls, be sure to keep them in an environment where they will receive low to moderate light and access to fresh water. It is also important to keep water temperatures in the right range (between 68°F and 77°F for ideal growing conditions, even though they can survive much colder and slightly warmer temperatures) as the wrong temperature can cause stress on the moss balls and could lead to slowed growth or browning.

Common Problems with Marimo Moss Balls

Despite their low maintenance requirements, there are some common problems with marimo moss balls that can arise. These issues include floating, color change, developing brown spots and nutrient deficiency. To keep your marimo moss balls healthy and thriving, it is important to be aware of these common problems and take the necessary steps to address them. 

Floating can happen due to trapped air bubbles in the plant as a result of its normal life cycle, which can be remedied by giving the marimo a gentle squeeze to pop the air bubble, allowing it to sink again. Honestly, though, you don’t really need to do anything, because it is normal and healthy for your marimo to occasionally float.

Color change is also a common problem, with the marimo turning brown, black or white. This can be caused by poor water hygiene and low light levels. Brown spots can also develop due to inadequate water hygiene (e.g. debris settling on your marimo) or low light levels. White spots or whitening can be caused by too much light (e.g. direct sun).

Marimo turning black is an indication of rot, and should be immediately addressed. Remove your marimo, wash it in a bucket of dechlorinated water with a few quick swishes and a gentle squeeze. Put it in a new container full of dechlorinated water with a pinch of ocean salt under low light, away from direct sun.

Finally, nutrient deficiency can lead to discoloration, stunted growth and withering of the marimo moss ball. The preferred habitat for marimos is believed to be lakes with moderate to high calcium levels, so replicating that environment in your aquarium by adding a source of calcium (such as cuttlebone) may help. 

To ensure your marimo moss ball is healthy and happy, make sure it is in an environment that is conducive to its needs.

Removing Algae from a Marimo Moss Ball Aquarium

Removing Algae from a Marimo Moss Ball Aquarium
Keeping your Marimo Moss Ball aquarium clean is essential to the health of your aquatic life. Algae can grow quickly and can be difficult to remove once it has taken hold. Luckily, there are some simple steps you can take to keep your Marimo Moss Ball aquarium free from algae.

The first step is to make sure your aquarium is properly lit – meaning that you aren’t running your lights too long or exposing your aquarium to sunlight. The fewer plants you have, the less often you should be running your aquarium lights. This will help to prevent any excess algae growth. 

Additionally, you should only feed your fish what they can consume within a few minutes. This will help to prevent overfeeding, which can lead to algae growth.

Next, you will want to check the water parameters of your tank and make sure they are in the optimal range for the fish and aquatic plants. You can do this by testing the water with a test kit or by getting it tested professionally. Excess amounts of trace elements such as phosphorus can lead to algae taking over your aquarium. If the water parameters are not ideal, you may need to do a water change of 30-50% per week for a few weeks to get it back under control.

If your marimo is the only thing in your aquarium, a 100% water change is fine.

Finally, you can remove any existing algae from your Marimo Moss Ball aquarium’s glass and other hard surfaces. This can be done by using a scrub brush or other cleaning tool to gently remove the algae from the tank walls and decorations. Avoid using chemical algae removers at all cost – they will kill your marimo.

The UV algae killing devices are fine, though.

By following these steps, you should be able to care for your marimo and keep them healthy and happy for decades to come.

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