Can Goldfish Live with Moss Balls?

Live plants are extremely good for fish tanks. Not only do plants look beautiful, but they take up nitrates from the water to use as nutrients, helping to keep the environment safe and clean for your goldfish.

The main issue with keeping living plants in a goldfish tank is that goldfish are notorious for digging and uprooting plants, and they also have habit of nibbling on new shoots and leaves. 

Well, the good news for frustrated goldfish keepers is that you can keep Marimo moss balls in a goldfish tank instead of using regular aquatic plants.

Read this guide to learn everything you know about keeping Marimo moss balls in your goldfish tank.

What are Marimo moss balls?

Indoor fish tank with plants

Marino moss balls are found in freshwater lakes in certain locations, including Iceland, Japan, Scotland, Estonia, and, more recently, Australia. 

Marimo is a Japanese word that means “seaweed ball.” However, these bright green spheres are neither moss nor seaweed but a rare form of algae. The balls are comprised of a spongy mass of algae that grows slowly outward at a rate of just a few millimeters every year, until the ball eventually reaches between 8 and 12 inches in diameter.

Moss balls are extremely hardy and virtually impossible to kill, making them perfect for a goldfish tank!  What’s more, these incredible living spheres can survive for more than one hundred years!

Can moss balls survive in a fish tank?

Yes, Marimo moss balls do incredibly well in aquariums. Although they prefer cooler water and a low flow, these are very low maintenance plants that you can keep successfully in both freshwater and brackish environments.

Do goldfish eat moss balls?

Although your goldfish and other livestock will enjoy nibbling fragments of leftover food from the surface of the fluffy algae balls, the fish won’t eat them. 

I kept a collection of moss balls of different colors and sizes in my large Fancy goldfish tank for many years. The fish seemed to enjoy pushing the balls around the substrate and rooting about underneath them, which they could do without causing any damage. However, I never witnessed my fish attempting to devour the balls!

Can moss balls harm goldfish?

Marimo moss balls are non-toxic and completely harmless to your goldfish. In fact, keeping a few of these weird looking objects in your goldfish tank can be extremely beneficial for the water conditions and for your fish, and we will discuss that later in this article. 

That said, a determined goldfish could rip off a piece of moss ball and swallow it, potentially leading to intestinal blockage or digestive issues. So, I recommend that you place only one Moss ball in your goldfish tank to start with and monitor your fishes’ behavior around it. 

If you spot the goldfish attempting to bite off pieces of the moss ball, I recommend removing the ball and providing alternative enrichment items for your fish.

Pond plant

Can you put moss balls in a goldfish tank?

Yes, moss balls typically do very well in a goldfish tank with minimal maintenance being required to keep them looking good.

I recommend removing the moss balls from the tank once every couple of weeks and squeezing all the moisture from them. Rinse the balls in tank water to remove accumulations of dirt and debris, and then replace them in the aquarium. 

Moss balls tend to drift around on the substrate with the current generated by your filter outflow. That, and nibbling fish, can distort the balls’ shape, so while you’re cleaning them, you can use the opportunity to reshape the moss balls by simply rolling them around between your two palms.

Note that it can take a few minutes for the balls to absorb enough water to sink again once you return them to the aquarium.

Do moss balls help fish tanks?

Marmo moss balls are highly beneficial for goldfish tanks for the following reasons.

Clean the water

Goldfish produce a lot of waste and, although your aquarium filter system will deal with ammonia and nitrites, the nitrates that are the end products of the nitrogen cycle can still harm your fish if levels rise above 20ppm.

Although maintaining your filtration system and carrying out partial water changes every week helps to control the nitrate levels in the water, living plants and algae, such as moss balls, also help.

The moss balls take up a nitrates from the water to use as nutrients and also absorb small amounts of debris, ammonia, and phosphates.

Oxygenate the water

As part of the process of photosynthesis, moss balls absorb CO2 from the water and release oxygen. 

That is a big advantage in a goldfish tank since these are very oxygen-hungry fish that use a lot of dissolved oxygen.

Require little maintenance

Moss balls are pretty much maintenance free; all you need to do is clean them gently as described earlier. 

The balls don’t need fertilizer or extra CO2 because they will feed on the waste produced by your goldfish. You don’t need to trim moss balls since they grow extremely slowly and in a uniform way, gradually increasing in size over many years, while maintaining their fluffy velvety appearance.

Control algae blooms

Moss balls can help to control algae growth in your aquarium because they utilize the same nutrients as other species of algae, making it much more difficult for nuisance plants to survive and spread.

Carry beneficial bacteria

Your biological filter media and tank substrate both provide a surface on which beneficial bacteria colonies can grow. 

Those bacteria are essential since they process the pollutants in the water and keep the nitrogen cycle ticking over. If you’re starting a new tank, Moss balls make ideal seeding material because they carry beneficial bacteria on their surface.

Easy aquascaping

In their natural environment, the moss balls are shaped by the water current constantly moving them around on the lake bottom. That movement also exposes the whole ball to light, preventing dead patches from forming and keeping the plants healthy. 

In a Fancy goldfish tank, the current is likely to be much slower, so the moss balls will lose their shape over time. All you need to do to keep the balls looking good is take one in the palm of your hand and carefully roll it around. No additional trimming or pruning is necessary.

Tolderates high pH

Most aquarium plants don’t like water that has a high pH. However, Marimo moss balls will happily tolerate a pH rof between 6.0 and 8.4 and still remain healthy.


Regular aquatic plants tend to shed their leaves and grow new ones. unfortunately, that means you need to remove all the dead matter from the water before it begins to decompose and pollute your tank. 

Marino moss balls do not shed!  As long as the algae remains healthy, the balls will be fluffy, vibrant green and remain intact.

Tolerate aquarium salt

Regular aquarium plants do not appreciate salt being added to the water. Sometimes, you will need to use small dose of aquarium salt to treat minor injuries, etc, which is, therefore, a problem. 

However, moss balls will happily tolerate salt and can even live in a brackish or saltwater environment where other aquatic species would fail.


Close-up Photo of a Goldfish Swimming Underwater

Goldfish enjoy digging around plant bases, frequently uprooting regular aquarium plants so that you’re forever having to replant them. In addition, goldfish are not averse to eating new shoots and tender plant leaves, destroying fragile plants and leaving your tank looking tatty and untidy.

Moss balls don’t need to be anchored, simply rolling around the substrate in the filter outflow current. Just remember to clean underneath the ball when you’re vacuuming the substrate as part of your regular maintenance routine.

Almost indestructible!

Marimo moss balls are virtually indestructible! Provided you don’t put the moss balls in chlorinated water or in an environment with very bright lighting, they should be fine. 

If you spot white flecks on the moss balls, that can indicate too much bright light, while brown patches mean that the lighting is inadequate.


Most regular aquatic plants self propagate or spread, eventually taking over your whole aquarium unless you regularly prune them or thin them out.  

In contrast, Marimo moss balls grow incredibly slowly even when given ideal growing conditions and a ready supply of nutrients, so you need not worry that you will end up with enormous green spheres filling your whole tank within a matter of months!

Simple propagation

Moss balls are incredibly easy to propagate. All you need to do is tear a small piece of an existing ball, roll it into a small sphere, and add the new plant to your tank. 

The main downside to that is that the moss balls grow incredibly slowly. For that reason, I prefer to buy a few new moss balls unless I want really tiny ones for aesthetic reasons.

How to keep moss balls in a goldfish tank 

Moss balls are extremely easy to keep in a goldfish tank, and here are some guidelines to help you. 

  • When choosing moss balls, always buy them from a reliable source and do not collect them from natural habitats. The balls should be bright green and fluffy with no brown or white patches.
  • You can position the moss balls on the substrate or attach them to driftwood or rocks if you want to. Just be careful not to obstruct your filter outflow or inlet pipes or take up too much of your fishes’ swimming space.
  • Moss balls don’t need very bright lighting and can live happily in dappled shade provided by taller plant species if necessary.
  • Moss balls are not fussy when it comes to pH, water hardness, and temperature, and mine did very well in my goldfish tank setup.

When it comes to maintenance, all you need to do is wash the moss balls in tank water every couple of weeks to get rid of any gunk and debris they’ve absorbed and reshape them if necessary.

Final Thoughts

I hope you enjoyed our guide to keeping moss balls with goldfish. If you did, please hit the share button before you go!

Marimo Moss balls make a great addition to a goldfish fish tank!  Moss balls are very slow growing so they won’t take over your tank like some aquatic plant species do. Goldfish can be very destructive, eating and uprooting aquatic plants, but Moss balls are virtually indestructible, even for feisty goldfish. 

Moss balls enjoy cold water conditions and require next to no maintenance, making them the ideal choice for a beginner’s tank.

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