How Many Moss Balls Per Gallon: Size, Benefits & Care

Here is the ideal amount of how many moss balls you can add to your aquarium per gallon, and the 11 benefits of doing so.

You may have heard of people adding moss balls to their fish tanks, ones such as Marimo Moss Balls. Yes, these mossy balls can be very beneficial for fish tanks, and this is true for many reasons. That said, how many of them should you get?

How many moss balls per gallon you can fit in your aquarium is actually quite high. Depending on the size of the moss balls in question, you could add anywhere from 1 to 3 per gallon of water. Today we also want to take a closer look at these moss balls and what they can do for your fish tank.

What Does A Moss Ball Do For A Fish Tank?

Moss balls bring a whole lot of benefits for a fish tank besides looking cool. We will get into more detailed explanations of the various benefits of moss balls in a section further below.

However, to sum it all up, moss balls help filter and oxygenate the water, they make for good play toys and scavenging grounds for fish, and they help to prevent algae buildups too.

Can You Have Too Many Marimo Moss Balls?

It is definitely not recommended to have more than 3 moss balls per gallon of water. However, this is all subjective and it’s really a judgement call on your end. It depends on how many other plants you have in the tank and how many fish you have.

Remember that everything in your aquarium needs room to thrive. For instance, if a fish needs 2 gallons of tank space, but you have 6 moss balls, it’s going to decrease the overall space available to the fish.

Therefore, what we can say here is that how many moss balls is too many is a matter of common sense more than anything else.

How Big Do Moss Balls Get?

When they grow in their natural habitat, moss balls such as Marimo moss balls can grow up to a whopping 12 inches in diameter. Now, you can see that due to their large size, you really can only have a limited number of them present in a fish tank.

That said, in home aquariums, moss balls will rarely grow larger than 5 inches in diameter. Also, remember that they will take a very long time to grow to this size, as they grow at about 5 mm per year, which is half a centimeter, or about 1/5 of an inch per year.

Benefits of Using Moss Balls in Your Tank

There are very many benefits that are associated with having moss balls in your fish tank. Let’s take a look at all of the reason why you may want to consider adding some of these cool looking things to your aquarium.

benefits of moss balls

1. Water Filtration & Pollution Absorption

One of the biggest reasons why people add moss balls to fish tanks is due to water filtration, particularly the absorption of contaminants.

Moss balls are very dense and have a lot of vegetation to them, and all of that green has the ability to absorb a lot of phosphates, nitrates, ammonia, solid waste, and other debris floating around in the water.

This helps to keep the water quality at a high level, it’s much healthier for the fish, and it also helps take some of the strain off of your aquarium filter.

2. Beneficial Bacteria

Another reason why moss balls are beneficial for aquariums is due to their ability to house a whole lot of beneficial bacteria.

Moss balls will usually already have a good amount of bacteria on them when you put them in the tank, plus they can also hold onto and allow more bacteria to grow.

These beneficial bacteria are essential for breaking ammonia down into nitrites, and then into nitrates, with each respective one being less harmful to your fish. In other words, moss balls allow for increased biological filtration in aquariums.

3. Oxygenation

Moss balls are also great at producing oxygen. Just like other plants, moss balls engage in photosynthesis for their own growth, a process which produces oxygen.

Therefore, the more moss balls you have in the fish tank, the more dissolved oxygen will be present.

This will help your fish breathe easier, and if you have enough moss balls, you may not even need an air pump and an air stone.

4. Resilient

Although it’s not exactly a benefit for the tank, this is a benefit for you. Moss balls are extremely resilient, almost harder to kill than they are to keep alive.

They can handle fairly unclean water, they aren’t picky in terms of temperature, they can handle varying pH levels, and they don’t need to be fed either.

5. Parasite Free

Something else that stands out about moss balls in fish tanks is that they are generally free of parasites and unwanted hitchhikers.

Many aquarium plants come complete with parasites and other unwanted things, such as small insects and larvae, all things which you don’t want in your tank.

However, for some reason, moss balls tend to not have any of these things on them. Therefore, they make for great aquarium plants with a very low risk of contaminating the water upon arrival.

6. Floating

Yet another cool thing about moss balls is that they are floating plants. This means that you don’t need to worry about attaching them to rocks or driftwood, and what kind of substrate you have in the aquarium is completely irrelevant too.

They are just really easy to deal with in this way as they do not need to be planted at all.

7. Preventing Algae

Something you may not know here is that moss balls are technically speaking a form of algae. If you have a fish tank, algae is something that you have probably dealt with. It spreads fast and it can quickly kill off everything else in your aquarium.

However, moss balls are a really friendly form of algae, as it grows just like regular moss anywhere else. It does not spread like other forms of algae.

Seeing as moss balls absorb all of the nutrients which other types of algae require to bloom, they can prevent algae blooms from occurring.

8. Salinity Tolerance

Although maybe not beneficial for every tank per say, what is notable about Marimo moss balls is that they can survive in waters that are fairly salty.

Although they may not be ideal for things like reef tanks, moss balls can be used for aquariums with brackish water.

9. No or Little Maintenance

What’s also nice about moss balls is that they really don’t require any maintenance at all. You don’t have to trim them because they grow super slowly.

You don’t need to provide them with CO2 or nutrients. Moreover, they can survive in varying water conditions and don’t need much light either.

10. Aquarium Inhabitants Love Them

A good reason to add some moss balls to your fish tank is that fish and other aquarium inhabitants really like them.

Some fish like to push them around the water, or in other words, they make for good play balls.

Moreover, the dense nature of moss balls means that they hold onto a lot of uneaten food and other debris, thus making them great places for fish and other aquatic creatures to scavenge for food.

11. Snail Proof

Something that many people appreciate about moss balls is that they are snail proof. If you have snails in your fish tank, you may have noticed that they like eating plants.

However, for one reason or another, snails do not seem to enjoy eating moss balls.

Types of Moss Balls

Generally speaking, there is really only one type of moss ball out there, particularly when it comes to use in aquariums.

First off, what needs to be said is that Marimo is a type of algae, and this can grow in 3 different ways. Epilithic Marimo grows on the shady side of rocks.

The second type of Marimo is a free floating type that forms into muddy carpets at sea beds.

The third type is the Marimo moss ball.

How To Care For Moss Balls

Caring for moss balls is really not very hard at all. Below we have a few moss ball care tips to ensure that your moss balls stay alive and healthy for as long as can be.

  • Marimo moss balls should not be kept in direct sunlight as this can actually harm them over time. They should be kept in indirect sunlight.
  • Moss balls do best in fairly cool waters. They do not prefer warm water, although they can survive in it.
  • Moss balls can grow to 12 inches in diameter, although they grow very slowly. Eventually, you may need to trim the outsides of them to keep them at an ideal size for your aquarium.
  • They do not require any extra CO2, food, nutrients, or fertilizers.
  • Moss balls absorb a whole lot of waste. While they can contain all of the waste they absorb, they cannot process all of it. Therefore, when you do water changes in your aquarium, make sure to take the moss balls out, rinse them in water, and squeeze them out.
  • To avoid having the underside of moss balls turn yellow, which they will do, try to rotate them on a regular basis, just so that any one area is not on the bottom for too long.
  • Try to never put moss balls in a goldfish tank, as goldfish will destroy them.

Commonly Asked Questions

Do Moss Balls Need Food?

No, moss balls do not require any extra food or nutrients. Everything they need to survive will be present in your aquarium.

Why are my Moss Balls Floating?

If you notice that your moss balls are floating, it is more than likely because they have an air pocket trapped inside of them.

To make them sink, gently squeeze them to get rid of the air pocket.

How Many Moss Balls in a 55 Gallon Tank?

As mentioned in the beginning, you can have up to 3 moss balls per gallon of water.

However, when it comes to a 55 gallon tank, this would mean having 165 moss balls, which is obviously too much.

Simply put, this is a judgement call on your end. Always leave enough space for your fish and other plants.

Do Bettas Like Moss Balls?

Betta fish are not huge fans of moss balls, but they also don’t dislike them. In fact, some betta fish can be quite playful and may move them around like a ball. If you need some ideas we have covered our favorite 10 betta plant suggestions here.

Do Moss Balls Help Cycle a Tank?

Yes, because moss balls can hold onto so many beneficial bacteria, bacteria which help spur on the nitrogen cycle in a fish tank, they therefore help cycle tanks.


Moss balls can have very many benefits for a fish tank, and we would definitely recommend considering getting some for yours.

They help keep the water clean, fish love them, and they look super cool too, not to mention that they are very low maintenance.

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