Marimo moss balls have been marketed as “betta buddies”, but given that they are a relatively recent addition to mainstream fish keeping, many people are confused as to what they are. Is it a type of moss that grows underwater? Will it rot? Why are they sold as “betta buddies” rather than, say, “goldfish buddies” or “platy buddies”?
Marimo moss balls naturally occur in Japan, and Marimo is actually Japanese for “moss”. Despite the fact that their name is “moss moss”, Marimo moss balls are actually a form of spherical algae. Their shape is formed by rolling across the bottom of a cold lake. While the term “algae” may scare an aquarium keeper, this type of algae functions more like a plant than something invasive.
In this article, we will discuss whether or not moss balls are good for bettas, their primary uses, cutting moss balls in half, whether moss balls can be dangerous, Marimo and cycling, Marimo life spans, do Marimo produce oxygen, and how many Marimo you should keep per gallon.
Are Moss Balls Good for Bettas?
Marimo moss balls are able to reduce some of the nitrates in the tank and increase some of the oxygen levels just as any other plant would. In addition, some bettas like to roll the smaller ones around the tank, which gives them some activity.
While they are gorgeous, they do not cause much of an impact on the overall tank chemistry. They do have some perks, but a betta would be just as happy with one or without one (excluding bettas who view them as toys, as they are happier with moss balls).
What are Moss Balls Used for?
Moss balls are primarily used for decoration in betta tanks, though they are very useful in shrimp tanks. Their beautiful shade of green is not often seen in plants, especially plants that are as easy to care for as Marimo.
Some bettas also like to use the moss balls as hiding areas. While it is best to provide your betta with many different hiding areas, some may end up preferring to hide behind a small wall of Marimo moss balls. If you have enough to stack them, your betta may start swimming in and out of them.
Can you Cut a Moss Ball in Half?
While it may seem like a bad idea, cutting a Marimo in half is an easy way to propagate them. Propagating a plant, or in this case, an alga, means to create more of that plant. Marimo typically reproduces by budding or growing a smaller alga ball off of the parent algae, which detaches after it has grown a certain bit. It can take decades for a Marimo to naturally reproduce, so many keepers split their moss ball in half to speed up the process.
Once you cut your Marimo, roll both halves gently to reform a spherical shape. Once you have formed them, simply place them back into the tank. Voila! You now have two Marimo moss balls.
Can Moss Balls Kill Fish?
The answer to this question is both yes and no. A properly cared for Marimo can only have positive effects on an aquarium. However, if you neglect the Marimo, it can release massive amounts of toxic ammonia, which can kill your fish.
Marimo moss balls roll around and collect debris. Even if it doesn’t roll around your aquarium, it will collect debris and mulm. Just like anything else that collects debris (for example, the filter media), your moss ball needs to be cleaned. Cleaning it weekly while doing your weekly water change is a good habit.
Simply squeeze it into a bucket of aquarium water a few times and reroll it if it loses shape. This clears it of debris, which can reduce the number of harmful nitrogen compounds in your aquarium (ammonia, nitrite, nitrate).
In addition to cleaning it, you need to rotate the moss ball every few days to prevent it from rotting. They naturally roll around in their native habitat, but this is rarely replicated in aquariums. By rotating it, this ensures that the moss ball receives even light all over, preventing rot.
Sometimes a moss ball doesn’t respond well to the aquarium water and can become ill. If you notice your Marimo losing vibrancy, turning yellow, or turning gray, remove it from the tank, clean it, and place it in your fridge overnight. After placing it in the fridge, put it in a clear bowl or clear cup (still submerged in dechlorinated water) and put it by a bright window for one to several days.
If the moss ball rots in the aquarium, it will begin producing toxic ammonia in high levels. If left in the aquarium for an extended period of time, it can be fatal to bettas.
Can Moss Balls Help Cycle a Tank?
Moss balls can gather and hold many different types of debris, including some types of bacteria. When you cycle a tank, you are building up certain bacteria colonies that convert toxic nitrogen compounds to less toxic ones. While these bacteria live on all surfaces in an aquarium, including moss balls, roughly 90% live in the filter.
If you have a moss ball in an established tank and move it to a new tank, it will carry some of those bacterial colonies over. They can help speed up the cycle of a tank by adding bacteria that convert nitrite to nitrate, as that bacteria isn’t often present when a tank begins to cycle. While it won’t have a huge impact, it can decrease the amount of time to cycle a tank by a few days to a week.
How Long Do Marimo Live?
Betta fish need warm aquariums and generally require slow water flow. Marimo is able to thrive in these water conditions, and the low flow allows them to collect particulates they can feed on. However, their natural habitat has cold water and high flow. Despite this, it appears that they are capable of reaching their full life span in aquariums.
In all technicality, we don’t know quite how long they can live in aquariums. In their native areas, many of the moss balls are over 100 years old, and we haven’t had aquarium heaters around for that long. Due to this, we haven’t been able to fully measure the impact of increased heat on their lifespans, but so far there have not been any issues.
Do Marimo Produce Oxygen?
Unlike many types of algae found in aquariums, Marimo actually produces oxygen rather than consuming it. This increases the amount of dissolved oxygen in the aquarium, which is beneficial to your betta. It is also a sign of the Marimo consuming some of those harmful nitrogen compounds.
How Many Marimo Per Gallon?
Unlike most other plants, Marimo are not heavily dependent on the amount of fish waste and nutrients available. This is primarily due to how slowly they grow (roughly half a centimeter per year) and how much they rely on light. If you provide a good deal of light and only a little bit of nutrients (or just simple fish waste), you will be able to keep several Marimo per gallon.
There is not a set rule of thumb when it comes to keeping Marimo, but somewhere between 1-3 per gallon is around the maximum you should keep. Some people have had success with more, some people struggle with one per gallon. You likely won’t know until you get them, so it is better to start with just a handful and go from there.
In conclusion, Marimo moss balls can benefit your betta. They can produce oxygen, remove some toxic nitrogen compounds, and can help cycle your tank if they were kept in a previously cycled tank. Marimo is very easy to care for and can add a lovely splash of green to your tank at a very minimal cost.