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Marimo Moss Balls – The World’s Easiest Aquarium “Plant”

Do you lack a green thumb when it comes to keeping live aquarium plants? Or maybe you want to add a touch of nature to your betta fish tank without a lot of effort? Let me introduce you to the marimo moss ball. This velvety green orb is neither a moss nor plant, but a species of green algae known as Aegagropila linnaei that gets its unique shape from tumbling about the bottom of freshwater lakes. The nickname “marimo” roughly translates from Japanese as “water plant that’s kind of like a bouncy ball.”

Care Instructions for Marimo Moss Balls

When you first get your marimo ball, rinse it in aquarium water, place it in the tank, and you’re done! It may float at first but should eventually sink once it becomes waterlogged. They appreciate low to medium light, so keep them out of direct sunlight. Most articles recommend growing moss balls in cooler temperatures because of their native habitats, but many hobbyists have seen success keeping them in betta tanks with temperatures as high as 80°F.

As for maintenance, I recommend lightly rolling the marimo ball in your hands every time you do a water change so that it won’t lose its shape. Also, flip it around occasionally so that all parts of the algae get access to light and won’t start browning.

marimo moss ball and red cherry shrimp


Clean-up crew like freshwater shrimp, snails, and invertebrates are pretty good about picking off any leftover food that gets caught in the moss ball. However, if it starts collecting detritus, take it out of the tank, remove any undesirable algae, and gently swish it in a bucket of aquarium water.

How to Grow More Moss Balls

The good news is that marimo balls are very easy to propagate. Simply squeeze the water out of your moss ball and cut it in half with a knife or scissors. Roll the new clumps in your hands to form little spheres, and tie some cotton sewing thread around them to maintain the shape. Tada, you’ve doubled the number of fuzzy green pets you have!

The bad news is that they grow at the slow, slow rate of 0.2 inches (or 5 mm) per year. In Japan, wild marimo balls can reach 8 to 12 inches in diameter, but most commercially available versions are sold at 2 inches or smaller. (So, if you ever see a really large moss ball in an aquarium, you know the owner deserves mad props because it took ages to get that big.) Some sources recommend using fertilizers and CO2 injection to increase growth rate, but for me, it’s just faster to buy another one.

aquascape using marimo moss balls in the foreground


The Many Uses for Marimo Balls

My final suggestion for marimo balls is that they don’t have to live only as spheres. In nature, Aegagropila linnaei also grows as flat mats on rock surfaces, free-floating filaments, or shaggy sheets on the lake floor. Therefore, aquascapers have gotten very creative with their moss balls, unrolling them into thick carpets, draping them on hardscape, or flattening them to make underwater bonsai trees. Other people don’t even put their marimo balls in fish tanks, but rather place them in beautiful jars to serve as home decor. So, whether you want an undemanding “house plant” or a little tankmate for your fish, you won’t find anything easier to care for than this ornamental algae.

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