Thursday, May 1, 2014

How-to Guide: Taking care of your Marimo

When I first saw pictures of marimo a couple years ago, I had no idea what they were. I was hoping they were sentient and would roll to you and be fun. I looked up videos and they don't do much besides sit there, make bubbles and occasionally float up to the surface. Although they might not be as lively as I originally thought, I'm very happy about owning such an attractive plant ball. They're very soft to the touch and are a nice addition to my fish tank.

Marimo are sometimes called moss balls, but they are actually green algae. Their natural habitat is in deep freshwater lakes in Japan and Iceland. Marimo do not have many requirements for living, so that makes them an ideal plant to take care of. They're perfect if every plant you've ever had died on you (like mine have). Although they are low maintenance, that doesn't mean you can just forget about them completely.

Where to buy

They have become more available in online, on sites like Facebook and by fans of anime you may log on to this website to find out more about Marimo (Official Website)

Most major pet stores carry marimo. They cost about $8 USD at PetCo and PetSmart. It was rumored they were selling illegitimate ones in the past, but the ones I've seen lately are real. You can also find them (usually nano-sized) in cute containers on Etsy.


Although they are found in deep cold waters, room temperature (25 °C  or 77 °F) tap water is good for your marimo. Change the water more often in the summer and less in the winter. I change the water for mine every week but I also have a fish dirtying up the tank to think about. I would say every 2-3 weeks in the winter would be fine, but make sure you don't forget about it! If your water looks cloudy that is a sign you should change it.

A lot of sources debate whether distilled/filtered water is a better choice, but mine is doing fine with tap water and the minerals that come with it. It's up to you and the quality of your water.

They can't survive freezing conditions, so don't put them in your freezer either!


I usually bathe mine when I change the water once a week.

Fill up your sink or fill a bowl with cold water. In the water, hold your marimo in your palm and squeeze out the dirty water. If you squeeze too much, it will float so make sure you soak it some more before putting it back. Try to Gently rub it back into a ball if it comes out of shape.


Marimo are algae, so they need light to be able to thrive. It will die if exposed to too much direct sunlight.  Since they live so deep down in lakes, they are used to receiving very little natural sunlight. An artificial light source like a lamp is good enough for your marimo to go through photosynthesis.

Fish & other

A lot of people say that fish will eat them, but from my experience a betta fish is fine tank-mate. It's possible other types of fish might be harmful though, so be careful! I know gold fish like to eat algae, so it's probably not best to put them together.

My betta fish really likes my marimo. He lounges on it like it's a fuzzy beanbag chair.  My marimo usually is positioned against the side of the bowl and my fish likes to hide in the crack between them. Sometimes when my fish is going crazy he sends my marimo flying across the bowl. It's a very cute dynamic!!

Snails: Be careful because they usually like to eat algae. Apple snails should be fine, they prefer dead plants

Shrimp: They use their legs to burrow below the surface of marimo to dig up decayed matters to feed on. In the process, they help keep the marimo ball surface free of debris.

Size & Growth

Marimo sold in stores are about the size of golf balls or a little bigger. Marimo grow, but very slowly in domestic settings so don't expect much. 


Marimo reproduce by division, but they might not survive if you do it on you own. When they grow larger, they will naturally break apart so you should leave that to a professional (the marimo itself).


It's possible your marimo is producing a lot of oxygen (which is healthy), or you squeezed too much water out of it. If it's bothering you, just try and soak it until it's heavier. Maybe you should check if you bought a styrofoam ball wrapped with felt while you're at it.


As long as you take good care of your marimo, it could live up to 60 years! The actual lifespan is unknown. I can't wait to pass my marimo down to my children.