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Oranda goldfish, close up

Do Goldfish Need a Filter? Spend Your Money Wisely!

When I was setting up my first tank for two pet goldfish, I wondered: do goldfish need a filter? I quicky did my research and have learned a lot since. Here’s what you should know:

Quick Answer

While technically speaking, if the water is kept extremely clean, a goldfish may not need a filter, an aquarium filter is always recommended for goldfish and all other fish. Goldfish are fairly messy animals that release a lot of substances into the water which can be harmful if left untreated.

Keep on reading, as there’s more to this choice than just “goldfish are messy eaters”.

Do Goldfish Need a Filter?

You’ve probably seen people keep goldfish in nothing more than small bowls with water and maybe a little plant.

Seemingly, these goldfish survive and do just fine for a certain amount of time, but there are usually problems that cannot be seen by the naked eye, and this may result in the goldfish dying much sooner than it otherwise would.

Oranda goldfish, close up

Yes, it is true that goldfish are fairly resilient creatures that can adapt to their surrounding environments. This means that for the most part, goldfish can survive in varying pH levels, water temperatures, and within other parameters.

Therefore, technically speaking, as long as the water is kept very clean, a goldfish may not need a filter to survive.

However, this is a statement that could be said for all fish in all aquariums. Most fish do just fine as long as the water is kept clean, but the issue is of course that this is very difficult to do unless you have a filter.

After all, the whole point of a good aquarium filter is to maintain proper water conditions and water quality.

This is why I personally go against the so-called common knowledge of goldfish not needing filters, because the only real way to keep aquarium water clean is with a filter. Ultimately, goldfish living in dirty water can become very sick and eventually die, which is why I say that every goldfish always needs at least a decent filtration unit in their tank.

Why Do Goldfish Tanks Need Filters?

As I have established, it is best if you have a filtration unit for your goldfish tank, but why is this the case? Well, one of the biggest issues with goldfish tanks is that goldfish themselves are fairly messy eaters. Goldfish tend to leave a lot of uneaten fish food laying around in their tanks.

Goldfish are also pretty hungry creatures that eat a lot, and when fish eat a lot, they also produce a lot of waste. Both uneaten fish food and fish waste release various substances into the water which are unhealthy for fish.

The main substance I’m talking about here is ammonia. Even extremely low levels of ammonia can be very harmful to fish. The official recommendation is that fish tanks should contain absolutely no ammonia at all.

Small goldfish tanks that don’t have good filters, due to the messy eating habits of the goldfish, tend to have elevated ammonia levels, and that causes serious problems for fish.

In simplest terms, ammonia can quite literally burn your fish from the inside out and will quite quickly result in its death. Chances are that if you keep feeding your goldfish ample amounts of food, and you have it in a relatively small tank without a filter, the ammonia levels will build up to the point where it will be lethal for your fish.

Besides performing regular water changes, which you can only do so often and so much of, the only other way to remove ammonia from the fish tank is with a good aquarium filter.

What it all boils down to is that without a good aquarium filter, it is very likely that ammonia levels will build up in a small goldfish tank, ultimately resulting in the death of the fish.

Three Main Types of Water Filtration and Why They Are Important

Seeing as I keep recommending that you have a good aquarium filter for your goldfish tank, let me explain why exactly these filters are so important. It really all comes down to the three main types of water filtration that every aquarium needs, which a good aquarium filter should provide.

The three main types of water filtration your goldfish needs to be happy and healthy include mechanical, biological, and chemical filtration. Let me explain each of these in a bit more detail, so you know exactly what you’re getting into.

Mechanical Filtration

The first type of filtration that a good goldfish filter should engage in is known as mechanical filtration. This is where physical filters such as sponges and floss pads are used to remove physical debris from the water.

The type of physical debris removed by this filtration type includes any solid particles, whether this be uneaten fish food, decaying plant matter, fish waste, or anything in between.

This is very essential because removing these items from the water will stop them from decaying and from releasing ammonia and other harmful substances into the water. This is your so-called first line of defense.

Biological Filtration

The next, and perhaps the most important type of filtration that you need for your goldfish tank is biological filtration. Biological filtration involves what are known as beneficial bacteria. There are different types of biological filtration media out there, but the main point of all of them is to allow for large colonies of bacteria to grow.

These are very special kinds of bacteria that feed on ammonia and other such substances. They break down ammonia into nitrates, and nitrates into nitrates, with nitrites being much less harmful for your fish tank. Without adequate biological filtration for your aquarium, ammonia levels will continue to rise until your fish can no longer tolerate them.

Once again, remember that even extremely low ammonia levels are not tolerable by fish. Therefore, you need to ensure that you have proper biological filtration for your fish tank, or else it is likely that your goldfish won’t survive for very long.

Chemical Filtration

The third type of water filtration that is quite important for aquariums is known as chemical filtration, and this is usually performed by something known as activated carbon. 

Activated carbon has the ability to remove various unwanted substances from the water, with tannins being one of them.

Tannins are natural substances released mainly by things like driftwood and plant matter. The issue with tannins is that they can make water more acidic, and sometimes to the point where goldfish cannot handle it.

Therefore, removing tannins from the water with activated carbon is essential. Activated carbon may even be able to remove various discolorations, odors, and other unwanted substances, such as heavy metals, from the water.

Why You Should Never Keep a Goldfish Without a Filter

Let me quickly summarize all of the main reasons why not having a good filter in your goldfish tank is a very bad idea.

  • Uneaten fish food, decaying plant matter, and fish waste can all cause aquarium water to become very cloudy and look dirty. These substances can also cause foul odors.
  • A buildup of ammonia, which are a result of fish waste and decaying organic matter, can quickly cause severe illness and death in fish.
  • Other substances in the water, which may be introduced through your tap water, such as heavy metals, as well as tannins introduced by organic matter, can all have detrimental effects on the overall health of your fish.


While some people say that technically speaking, goldfish do not require filters as long as the water is kept clean, the caveat here is of course that keeping the water clean is virtually impossible without a good aquarium filter. Therefore, my official recommendation is to get at least a decent filter for your goldfish, just to help it stay healthy.

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