20 Gallon Goldfish Tanks

6 Best Filters for 20 Gallon Goldfish Tanks for 2024

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Many experts say a new, single goldfish should be allowed at least 20 gallons of water to roam around in and be healthy and happy. For brand-new goldfish pet owners, this raises a question: What’s the best water filter system for new goldfish?

We research and inspected numerous water tank filters for goldfish aquariums, and offer our tips and suggestions for what might best meet your needs at the 20-gallon level.


  • The Tetra Whisper 40i Internal Filter tops our recommendation for goldfish tank filters, for a number of reasons including affordable pricing and capacity to serve large aquariums.

Who Needs a Goldfish Tank Filter?

Those new to caring for goldfish will learn fairly quickly that this type of fish is not known as among the cleanest. They eat a lot of plant matter, and defecate often, so monitoring the water quality at all times is highly recommended.

Having a tank too small for a goldfish, or that’s filled with near-toxic water, can be detrimental toward the growth of your pet. And, frankly, its happiness!

An aquarium water filter helps much in this regard. Beyond the waste matter, also accumulating in a fish tank is the residue from converting oxygen. Basically when they breath out through the gills, it leaves miniscule amounts of exhaled waste much like the carbon dioxide we emit.

It’s hard to imagine any goldfish surviving long in the wrong environment, like a tank that’s too small, and especially one without a water filter.

Our Choices: Best Filters for 20-Gallon Goldfish Tanks

1. Best Filter for 20-Gallon Goldfish Tanks Overall ~ Tetra Whisper 40i Internal Filter


There is so much to like with the Tetra Whisper 40i Internal Filter for goldfish tanks, not the least of which is the affordable price and significant maximum of 40 gallons. New goldfish owners really can’t go wrong with this model, and for that matter many other offerings by Tetra.

It’s important to note that this model includes an air pump as well as the filter system, making it an all-in-one tank maintenance tool. The air-driven design filters up to 70 gallons per hour while at the same time oxygenating the water. Inside, the dual-sided mesh filters catch plenty of fish waste and other debris.

Note: Tetra Whisper also comes in models good for tanks up to 4, 10, and 30 gallons, but we like the 40i and its maximum 40 gallons.


  • Style: Clip-on (clip included)
  • Weight: 1.5 Pounds
  • Size: 5.13 inches by 5.88 inches by 10.5 inches tall
  • Special Feature: Bio-Bag cartridges

What We Like

  • Very nicely priced considering the quality
  • Ease of disposing Bio-Bag and replacing it

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2. Best Filter for 20-Gallon Goldfish Tanks Runner-Up ~ Marineland Penguin 150 Bio-Wheel Power Filter


Those looking for the very best regardless of price will appreciate the Marineland Penguin 150 Bio-Wheel Power Filter. It ranks among the top sellers of all fish tank filters, and for good reason. Advanced technology provides a multi-stage filtration process, which offers mechanical, chemical, and biological filtration in the tank.

The rotating bio-wheel alone adds a touch of real action to any aquarium; and we appreciate the brand’s easy-to-replace Rite-Size Filter Cartridges.

Note: This model comes in versions for up to 10, 20, 50, and 75 gallons. The 150 is for tanks with capacity for 20 to 30 gallons. They are actually divided by gallons per hour (GPH), with models ranging from 75 to 350 GPH.


  • Style: Submersible
  • Weight: 1.86 lbs.
  • Size: 8.25 inches by 6 inches by 7.38 inches
  • Special Feature: Patented Bio-Wheel technology

What We Like

  • Technologically advanced
  • Multi-stage filtration process for peace of mind

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3. Best Filter for 20-Gallon Goldfish Tanks Runner Up II ~ Aqueon QuietFlow 10 LED PRO Aquarium Power Filter


Goldfish owners paranoid about tank water quality might look closely at the Aqueon QuietFlow 10 LED PRO Aquarium Power Filter and its indicator light that flashes when water can’t flow through the disposable filter cartridge. How cool is it to get automatic help knowing when to change the cartridge?

On top of the cartridge filtration system, the Aqueon QuietFlow filters also provide chemical and biological filtration. The water pump is self-priming, so it auto-starts or restarts if power is interrupted and then restored. This model provides high flow rates to ensure the best dissolved oxygen content possible.


  • Style: Replaceable filter cartridge
  • Weight: 1.2 lbs.
  • Size: 6.4 inches by 6.3 inches by 3.8 inches
  • Special Feature: LED light to indicate when the filter cartridge needs replacing

What We Like

  • Convenience and peace of mind with the LED warning light
  • Internal pump design to reduce noise

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4. Best Filter for 20-Gallon Goldfish Tanks for Less Noise ~ Aqua-Tech Ultra Quiet Power Filter


The Aqua-Tech Ultra Quiet Power Filter excels at, well, being quiet. It’s in the model’s name! The focus here is on avoiding the droning noise of many fish tank filters, an attractive selling point for goldfish owners living in tight quarters like apartments or for those who have difficulty sleeping nearby.

Buyers also might notice the impressive sucking power of this unit, and a cartridge with a molded ribbed back to contact as much water as possible. This model also engages in biological filtration, with a bio-foam filtration system to remove toxic ammonia or nitrates.

Note: Available in models maximizing at 15, 20, 40, and 60 gallons.


  • Style: Bio-foam filtration
  • Weight: 1.6 lbs.
  • Size: 4 inches by 7.5 inches
  • Special Feature: Motor noise limited to less than 40 db.

What We Like

  • Reduced noise compared with other models
  • Sleek design

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5. Best Filter for 20-Gallon Goldfish Tanks on a Budget ~ Fedour Submersible Aquarium Internal Filter


The Fedour Submersible Aquarium Internal Filter sure packs a lot of attractive features for such a small price, if cost is an important factor in your search. This brand takes great pains to provide a lot of detailed information about this model, so take a peek.

The internal water filter-water pump combo packs plenty of punch with a flow rate up to 80 gph through a filter charged at up to 4 watts. Neat-looking detachable sprayer tubes add a nice touch creating a small wall of water, and even with this feature the overall model is quite noise-free. The filter can be adapted to use biochemical or physical filtration, a nice option.

Note: this model is offered in two set-ups, one for 1 to 20 gallons, another for 5 to 35 gallons.


  • Style: Submersible
  • Weight: 8.47 ounces
  • Size: 1.81 inches by 1.65 inches by 5.28 inches tall
  • Special Feature: Detachable sprayer tubes that create a curtain of waterfall in the process to oxygenate

What We Like

  • Neat underwater design with strong suction cups for attachment
  • affordable pricing

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6. Best Filter for 20-Gallon Goldfish Tanks for Appearance ~ Coodia Internal Green Water Killer Aquarium Filter Tank U-V Pump


Aesthetics means the look of something, and if that’s most important for your aquarium, then consider the sleek design of the Coodia Internal Green Water Killer Aquarium Filter Tank U-V Pump. Its slender vertical look won’t block visuals into the tank, plus it emits bubbles in a cool way!

This is about the sleekest filter-water pump combo you can find ~ and it cleans tanks up to 75 gallons. The built-in 5-watt water pump is powerful enough to handle all that water, plus it emits bubbles that look kind of like those fish emit, for the process to oxygenate the tank.


  • Style: Submersible
  • Weight: 1.65 lbs.
  • Size: 12.91 inches by 5.55 inches by 3.39 inches
  • Special Feature: 5-watt water pump

What We Like

  • Sleek visual appearance
  • Good for great range of tank sizes

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What Fish Tank Water Filters Do

Put simply, filters in fish tanks remove excess food particles, decaying organic matter floating around, waste coming from the fish, and chemicals from the water. All organic matter like floating plant leaves or parts, or uneaten food, produce ammonia as they decompose naturally.

Mechanical filters remove these particles before they can produce ammonia dangerous to your fish.

Fish excrete the poison ammonia directly into the water through their gills. Ammonia is produced when proteins are broken down into amino acids and again when proteins are made to build new tissue or repair the body of an animal.

While humans expel mostly nitrogen in their exhalations, plus a little carbon dioxide, fish exhale a lot of carbon dioxide. Depending on circumstances, like the temperature or cleanliness of the water, this exhaled waste can be turned to ammonia, too much of which is harmful or even fatal for goldfish.

Many fish tank filter models today also come with a helpful water pump. See below for more details on water pumps.

Features to Look for with Fish Tank Filters

When buying a tank filter to manage goldfish, know their breed, age, maximum size, and how many fish will be in the tank. Since it is generally accepted that 20 gallons is the minimum for a single goldfish, that’s an element you should look for first: will this filter handle at least 20 gallons?

From there, consider the profile ~ how the thing will look in your tank, whether vertical or horizontal, and sleek or thick. For aquariums with multiple fish, it might be wise to find a filter that is less noticeable, e.g. quite thin or short.

Then other details are, does it do anything to keep the noise of the motor down? Does it also come with a built-in water pump for aeration? Does it use replaceable cartridges, and if so, which size and type.

For the last item, if you have more than a single goldfish, you might look into pricing for the replacement cartridges, as goldfish are known to be quite messy so the filtering system might have to be changed more often than for other types of fish.

Then there is price. If you’re intent is to host only a single goldfish, and no other type of fish in that tank, you might not need pricey super-filters. Just make sure it can handle at least 20 gallons, as there are a lot of water filters out there for maximizing out at 3, 4, 5, 10, or 15 gallons.

Related Questions

Question: How exactly do fish produce ammonia in the water they live in?

Answer: Ammonia is created from the metabolism of protein, e.g. when breaking down food for digestion. A major waste product from fish, they emit most from the gills but also some from their urine and feces.

Q.: Is it important to find a filter model that also has a water pump?

A.: They can be purchased separately, but in broad terms it is greatly beneficial for your fish to have a water pump serving the tank. Pumps oxygenate the water, that is, makes it easier for your goldfish to get the oxygen they need to grow and thrive. Stagnant water is not the healthiest for fish ~ and goldfish are known to be on the messy side!