Do Guppies Need A Filter? (You might be surprised!)

Do guppies need a filter? Whilst it is technically true that you can have a guppy aquarium without a filter, adding appropriate filtration makes keeping guppies healthy a lot easier. If you are an inexperienced fish keeper, definitely add a filter to your guppy aquarium.

Eating Daphnia
Eating Daphnia

Guppies were one of the first fish I ever kept. 30 years ago I was given a 10-gallon tank with a small group of guppies. From that day on, I don’t think there has been a single day when I didn’t have at least one aquarium filled with guppies.

Guppies are incredibly popular in the freshwater aquarium hobby. They have been on the list of ‘Top Fish’ for aquarium keepers for decades. They are colorful and hardy and easy to keep and breed.



Do Guppies Need A Filter?

When asking yourself, ‘does a guppy tank need a filter’ you may have read other articles where the author says they don’t. Technically that is correct, but they don’t explain why.

In nature, clearly, the rivers, streams, and lakes don’t have filters attached to them. Instead, nature is in balance. To understand why that matters, let us start by taking a look at what an aquarium filter is and what it does.

An aquarium filter has two main roles. Firstly, an aquarium filter physically removes dirt and detritus from the aquarium. This is known as mechanical filtration.

A sponge or some other medium physically removes the dirt by catching and holding it as the water passes through it until we, the aquarium keepers, remove the dirt by cleaning the sponge.

Mechanical filtration can be in the form of a sponge, as in a ‘sponge filter’ or in multiple layers of sponge which are of different porosities, like in a canister filter. Usually, in a canister filter the water will first pass through a coarse sponge, which catches large particles of waste, then a medium sponge, which catches finer dirt particles, then finally a fine sponge that catches the tiniest particles.

Occasionally there will also be a layer of filter floss that catches and holds onto even the finest particles.

Mechanical filtration makes our water look clean. It means we can look into our aquariums and be proud of the water. We usually like it to be crystal clear, because to our minds, that means it is clean.

The second job of an aquarium filter is to clean our water biologically. This means allowing bacteria to break down the ammonia from the fish waste, firstly to nitrites and then again down to nitrates.

Ammonia is very harmful to fish, nitrite is fairly harmful and nitrate is only harmful when in large enough quantities. Our filters allow this biological process to take place by providing a home for the right sort of bacteria to live on. This home is known as the filter media.

Filter media can be just about anything, providing bacteria can live on it. Bacteria will grow on everything in the aquarium equally. It will grow on the glass, the gravel, the decorations, and the media in the filter.

Bacteria don’t care, providing water can pass over it, bacteria will thrive in the aquarium.

In my own fish room, I use a lot of Fluval filters, so I decided to write an article titled Are Fluval Filters Good?


So, What Does Nature Do Without A Filter?

The reality is, that nature doesn’t care about the water being physically clean. Instead of using sponges to remove detritus, nature either allows it to build up until some other process deals with it, like bacteria breaking it down, or other animals will eat it.

In nature, there are countless other creatures that will happily eat decaying leaves, uneaten food, and even fish poop. Nature uses other creatures to process the waste.

Nature also doesn’t need filter media, because everything in the river or lake has bacteria growing on it, and this bacteria breaks down the ammonia from the fish. Nature just uses the gravel on the river bed or the fallen trees lying in the stream or the rocks in the lake as media for the bacteria to live on.

So If Nature Doesn’t Use A Filter, Why Should We?

The reason we need a filter and nature doesn’t is because we typically massively overstock our aquariums. I have no idea how many fish live in the Amazon River, and I have no clue how many gallons of water the Amazon River holds, but I can guarantee, there are far fewer fish per gallon in the Amazon than in our aquariums.

We typically cram 50, 60, 70, or more guppies or tetras into a 30-gallon aquarium and expect them to be happy and healthy, which they can be, providing their water is clean and safe to live in.

So, Is It Ever Possible To Keep Guppies Without A Filter?

If you set your aquarium up in the right way, and you don’t overstock the aquarium, then technically, you can keep your guppies healthy without a filter.

If I keep just 5 guppies in a 40-gallon aquarium for example, and I have water movement in the form of a circulation pump or airstone, then they will probably survive happily without a filter.

There is enough surface area on the glass, the substrate, and the decorations to process the waste from just 5 guppies.

The problem comes when the number of fish increases and with it so dies the amount of waste that needs processing.

If I Want To Go Filterless, What Else Can Help?

If you are adamant about not having a filter, there are a couple of things you can do to help keep your aquarium water clean.

  • Add live plants: Live plants will absorb some of the fish waste. They will use the ammonia, nitrites, and nitrates from your fish poop to grow. This is one of the ways nature has evolved to deal with fish waste. The live plants will also help by absorbing carbon dioxide from the water and releasing oxygen back into it. The more plants you have, the more waste they will absorb. Also, consider choosing plants that grow quickly. A plant that grows a foot a day naturally requires more food than one which puts on a single leaf a month.

  • Change water more often: If you don’t have a filter, more regular water changes will naturally mean less waste in the aquarium. Water changes are the most efficient way we have to export waste from our tanks. I always recommend water changes of about 25% to 50% every 2 to 3 weeks when aquariums DO have a filter. That may need to increase to 25% to 50% every week without a filter.

  • Choose a suitable substrate: If we know bacteria grow on all surfaces in an aquarium, choosing a substrate with lots of surface area, like gravel, is better than choosing something which will compact and have a low relative surface area, like sand.

  • Feed better quality foods: Generally speaking, the better quality the food you feed your guppies, the less ‘filler’ will be in that food. Filler is essentially anything that bulks out the food but offers little or no nutritional value to your guppies. Filler in foods is just needless additional waste being added to your aquarium. In theory, if you only ever feed live foods to your guppies, there would be much less waste for your aquarium to have to process.
  • Limit the number of fish: Needless to say, the fewer fish you have, the less waste there will be in the first place. The less waste there is the less need for a filter your aquarium has. If you are determined to go without a filter, limit the number of fish you keep. Also, seriously consider keeping only male guppies, that way, the population won’t increase over time.

In Conclusion

Yes, it is possible to keep a guppy aquarium without a filter, but the reality is, that it makes the job much harder. A filter keeps your water physically clean and biologically clean. Adding a filter means you can keep more fish in the same size aquarium and you can spend more time enjoying your aquarium and less time servicing it.


About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James
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