Do goldfish need a filter?

You should always include a filter in your goldfish tank or pond.

Goldfish eat a lot and produce a lot of waste, which can pollute their water. Without a filter, your aquarium water will soon poison your fish.

What type of filter do goldfish need?

There are two basic types of filter: external filters and internal filters. As the names suggest, external filters sit outside your tank, whereas internal filters are submerged within the tank.

There’s not a “correct” type and goldfish can be kept in tanks that use either an external or internal filter. However, an external filter is usually worth the extra cost if you can afford one.

As they sit outside the tank, an external filter can contain more filtration media and can therefore do a better job of cleaning your water. External filters can also be hidden away in an aquarium cabinet to avoid interfering with the look of your aquarium and have the advantage of not taking up valuable space inside the tank.

Wondering what size tank a Goldfish needs, check out our guide here

What size filter do you need for goldfish?

Both external and internal filters are available in various sizes. However, it’s not the physical size of the filter that is important. It’s the “flow rate”.

Flow rate is the amount of water filtered per hour.

You should aim for an absolute minimum flow rate of 5 times the volume of your tank per hour.

Ideally, you should look to filter closer to 10 times the volume of your tank per hour.

For example, if you have a 20 gallon tank, your filtration system will be in the region of 100 to 200 gallons per hour.

It will be easier to reach a higher turnover if you use an external, rather than internal, filter.

Many types of filter – such as the Fluval U Series come in a range of sizes so that you can select the right filter for your tank.

Cleaning your filter

It is vitally important that you never clean your filter in tap water.

Instead, once or twice per year, you should rinse your filter sponges in water from the tank.

Take care to only rinse the sponges gently, rather than squeezing them too aggressively.

This is because cleaning your filter sponges in tap water, or squeezing them out too much, can kill the good bacteria living in the sponges. And killing this bacteria would be very bad for your fish!


The answer to the question “do goldfish need a filter?” is a very definite yes!

In order to take proper care of your goldfish, you need a filter of some kind.

This could either be an external filter or an internal filter, but we recommend using an external filter wherever possible.

However, it’s important to realize that installing any old filter is not enough to ensure clean water. It’s important to research the best filter for your goldfish tank.

You need to get a filter that turns over around 10x the volume of your tank per hour, make sure that you have a big enough tank, and always remove any excess food after feeding your goldfish.

Even with a filter, your water can quickly become toxic to your fish. This happens when your filter is too weak, your tank is too small, you leave food in the tank to rot, or you don’t do enough water changes.

3 thoughts on “Do goldfish need a filter?”

  1. I disagree that you need a filter. I’ve had goldfish for many years in both ponds and tanks without filters, and they are apparently doing fine since they won’t stop breeding and making babies that I have to give away. And I hardly change any water. Water plants take up the nitrates. The water in the pond can look pretty rank in the summer, but it’s always tested really well – no ammonia, nitrites or nitrates. For the pond, I make sure I don’t have too many fish, and I don’t feed them (there are enough bugs apparently). Goldfish are just carp, and they evolved in ponds that do not have filters.

    • Your comment is a particular scenario where your setup is self-sustainable, but is not the general case. Generally, any aquarium with live fish must have a filter, otherwise, the toxic waste will kill the fish in the tank.

      • Good comment Oscar,
        Some well established planted setups may be able to house fish without a filter, however, we always recommend a filter for general setups, especially to newcomers in the hobby.


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