7 Best Filters for 20 Gallon Fish Tank (2024 Review)

A quality filter is a must-have accessory for any aquarium. Your filter plays a crucial role in maintaining a healthy nitrogen cycle by removing waste and helping break down toxic compounds in the water.

However, the filter you use needs to be a good match for the size of your tank in terms of flow rate and filtration stages.

Read on to learn more about different types of filters and which product is the best 20 gallon filter. Here is a quick glance at my top recommendations:

What Type of Filter to Choose for a 20 Gallon Aquarium?

A 20 gallon aquarium requires a filtration system adapted to a midsize tank.

It’s important to choose the right type of filter and the right combination of filtration methods.

Different Filter Types

One of the most common types of filters you’ll find in 20-gallon tanks is hang-on-back filters. These filters attach directly to the back of your tank and use a tube to draw the water into a filtration chamber.

The water will go through one or more filtration steps before a pump sends it back into the tank.

Canister filters are another popular option. A canister filter is somewhat similar to a hang-on-back filter, but this type of filter sits outside of the tank. There are two pumps drawing the water out of the tank and pushing it back in, which means that pressurized water will go through the filtration media.

The water pressure can make canister filters more effective for removing debris, and it also increases the flow rate compared to a back filter. Canister filters are ideal for heavily stocked tanks since they can eliminate large quantities of waste. Plus, you can easily hide these filters.

Internal filters can be more aesthetic since these filters are fully submersible, which means you can hide them behind aquascaping elements. However, it’s not the best filter for a 20-gallon tank due to its limited size. 

You can also find sponge filters. These filters use an air pump that pushes water through a foam sponge that acts as a growing medium for beneficial bacteria and as a mechanical filtration stage. Unfortunately, it’s not the best aquarium filter for anything larger than 10 gallons.

Different Types of Filtration

With a canister or hang-on-back filter, it’s easy to add and remove filtration layers to customize your filtration system. You’ll find a mix of mechanical, chemical, and biological filtration media in most systems.

Mechanical filtration uses grids or membranes to catch debris and fine particles. A mechanical filtration stage is crucial for catching large debris, including waste that hasn’t broken down yet.

It also prevents large debris from clogging the filter. However, it’s not effective for compounds that have dissolved into the water.

Chemical filtration can react with waste and other compounds to neutralize them. Activated carbon is the most common type of chemical filtration media.

Biological filtration is an easy way of maintaining a healthy nitrogen cycle in your tank. You can use different filtration media to create an environment where beneficial bacteria can thrive and help break down ammonia and other toxic compounds.

Our Choice for Best Filters for 20 Gallon Fish Tanks

We feel confident recommending the following filters for maintaining your 20-gallon tank.

Check out these other top picks:

• Best Koi Pond Filters For 2024
• Best CO2 Diffuser for Your Aquarium
• The Best 10 Gallon Fish Tank Filters

1. Editor’s Choice: Aquaclear, Fish Tank Filter

This affordable and durable filter is an excellent option for novice and experienced aquarists alike. With its energy-efficient design, this 5W filter will also help keep your electricity usage down.

It’s a multi-stage filtration device that relies on a mix of mechanical, chemical, and biological filtration:

The water will first go through the AquaClear Foam element. This insert catches large debris and promotes the development of beneficial bacteria for the nitrogen cycle.

The next filtration stage is an activated carbon filter that absorbs impurities, including compounds that have dissolved into the water.

The water will then go through ceramic rings. With their porous surface and optimal contact area, these rings are ideal for beneficial bacteria to grow.

The filter also uses BioMax and Cycle Guard, two products that enhance your water quality.

The water will go back to the tank via a small waterfall. It’s an interesting feature because it reduces noise and helps oxygenate your tank.

Overall, this filter is very easy to use. You’ll have to clean it every two weeks and replace filtration media as needed. You can also customize the filtration stages by using different AquaClear products.

We like the transparent design of the filter because you can see the filtration compartment and any clogs.

You can also control the flow rate of the filter. For larger tanks, you can turn it up to 200 gallons/hour but lowering the flow rate means that some of the water will go through the filtration stages multiple times for a cleaner tank.

Pros:

• Multiple stages of filtration
• Easy to install and use
• You can adjust the flow rate

Cons:

• It’s difficult to hide the filter
• Customize the filtration stages can be intimidating for beginners

2. Runner Up: Fluvial C3 Power Filter

With a flow rate of up to 119 gallons/hour, this performing filter is ideal for 20-gallon tanks. It’s a compact filter that remains discreet in spite of its clip-on design.

You can use this versatile filter for freshwater and marine setups. We like the fact that you can adjust the flow rate and lower it to have the water go through the filter multiple times.

You can also adjust the length of the tube that sucks the water in. The filter has an excellent pump that will work well even if you increase the depth of the intake tube to avoid disturbing the fish.

There is also an indicator that tells you when it’s time to clean the filter. It’s a great feature for beginners who might be unsure of how often they should maintain their filter.

This quality aquarium uses several filtration stages. There is a large foam insert that will catch debris and prevent the filter from clogging. The next filtration stage is a polyester screen that catches finer particles.

Next, the water will go through an activated carbon medium that removes impurities and odors. The filter will then push the water through biological screens and ceramic nodes, two filtration stages that promote the growth of beneficial bacteria. The star-shaped ceramic nodes are noteworthy since their design enhances the contact surface with the water.

Pros:

• Five filtration stages
• Compact design
• The indicator makes maintenance easier

Cons:

• It makes more noise than other products

3. Best Value for the Money: Aquaeon QuietFlow Canister Filter

This canister filter delivers the best value for the money with its 200 gallon/hour flow rate. The fact that this canister filter uses pressurized water means it does a better job of cleaning the water. However, the price tag is higher than the other products we reviewed above.

You should still consider this versatile filter because of the exceptional value it delivers. It comes with all the components you need to connect it to a spray bar or another accessory for returning water to the tank. You’ll also get a clip-on attachment that works as a water polishing unit and that removes large debris to support the canister filter.

You’ll find three nested baskets inside of the canister element. The filter comes with mechanical, chemical, and biological filtration media that you can easily customize.

Pros:

• The accessories add value
• Impressive 200 GPH flow rate
• Pressurized water

Cons:

• The hose lines can be hard to clean

4. Alternative: Tetra Whisper EX 30 Filter

This affordable filter is ideal for beginners. It doesn’t require any priming and will start working right away. Plus, the design makes it easy to replace the different filtration elements so you can clean or replace them.

It’s a compact filter that you can clip on the back of your tank. It delivers a flow rate of 160 gallons per hour, which is suitable for most 20-gallon tanks. We also like the waterfall design since it helps add oxygen to the water.

This hang-on-back filter uses four different filtration stages. There is a first layer with floss that catch large debris. Next, the water will go through an activated carbon pad that neutralizes toxic compounds from waste.

There is a second layer with floss that catches fine particles, and a layer with bristles that host bacteria for biological filtration to remove nitrites and other compounds.

Pros:

• Affordable and easy to use
• Easy to access the different filtration elements
• Excellent flow rate at 160 GPH

Cons:

• The compact design limits the size of the contact surface
• Other filters have two biological filtration stages

5. Alternative: Fluval U3 Underwater Filter

This underwater filter is a great addition to your setup. An underwater filter can be more discreet since you can hide it behind rocks or driftwood. Plus, it allows you to seal your tank with a lid. It can also be quieter than external filters.

However, maintenance can be more challenging since you’ll have to remove the filter from the tank to clean it.

It’s a versatile filter that will work with freshwater and saltwater tanks. The great thing about this product is that you can set it up horizontally or vertically. Installing the filter vertically is ideal if you want to create currents and add more oxygen to your water.

On the other hand, placing the filter horizontally is convenient for small tanks or tanks with shallow water.

We also like the water output feature. You can switch between three output valves. You can have the water come out at the top of the filter to add more oxygen to your tank or select the bottom output to agitate the water near the substrate. There is also a spray bar in the middle that will oxygenate your tank without disrupting plant life.

This underwater filter uses a simple filtration system with three stages. There is a large foam pad that provides mechanical filtration, a poly-carbon pad for chemical filtration, and some ceramic nodes for biological filtration.

Pros:

• Set up the filter horizontally or vertically
• Great option for adding more oxygen to your water
• Three stages of filtration

Cons:

• Cleaning and maintenance can be more challenging
• Other filters have more filtration stages

6. Alternative: GRECH Sterilizer Hang-On Back Filter

This hang-on-back filter comes with a few additional features that make it worth considering. It delivers an adjustable flow rate of 211 GPH, which is higher than some of the clip-on filters we mentioned above.

The first noteworthy feature is the surface skimmer. This skimmer prevents the formation of films on the surface of the water.

The second interesting feature is the UV sterilization light that you can turn on and off as needed. We’ll discuss it in more detail below.

This filter uses a simple three-stage filtration method with mechanical, chemical, and biological filtration. There is a 5W pump that pushes the water through the filter, which helps increase the flow rate.

In theory, UV lights can kill microorganisms like pathogens, mold, yeast, and more. UV or ultraviolet rays have a short wavelength, which means they carry a lot of energy.

However, there are different types of UV rays. You need UV rays with a wavelength of 100 to 280 nm to effectively kill microorganisms. The manufacturer of this filter doesn’t have any information about the wavelength of the UV light present in the filter, which means it’s difficult to determine how well the filter will sanitize your water.

There is another important consideration about sanitizing your tank water. A UV light with a sufficient wavelength will eliminate algae, parasites, and unwanted bacteria.

However, you also need beneficial bacteria to help break down toxic compounds that come from waste. The biological filtration stage you’ll find in all the filters we recommend plays an important role because it promotes the growth of beneficial bacteria and introduces these microorganisms into the water.

If you activate the UV light, you’ll remove these microorganisms from the water and could disrupt the nitrogen cycle.

Pros:

• Surface skimmer
• UV light sterilization
• Three stages of filtration

Cons:

• There is no information about the wavelength of the UV light
• In theory, a UV light could kill beneficial bacteria

7. Alterantive: TARARIUM Aquarium Power Filter

This bang-on-back filter is a good budget option with its three filtration stages and its 158 GPH flow rate. It’s a good choice for beginners since it’s easy to install. Plus, you can open the back cover to access the different filtration media and replace them as needed.

There is a surface skimmer that adds value to the product. This feature prevents the formation of an oil or algae film on the surface of your tank. We also like the design of the water inlet tube that prevents injury to your fish.

This filter uses three filtration media. You’ll find a pad with cotton fibers that catch large debris, an activated carbon pad for chemical filtration, and a sponge that acts as a biological filter. We like the fact that this filter uses a sponge since the structure of the sponge will help catch debris the cotton fibers might miss.

Overall, it’s an affordable filter that is easy to clean and install. However, user reviews mention that the noise level is louder than what the manufacturer claims. A few shoppers also seemed to run into issues with the quality of the pipe fittings.

Pros:

• Easy to maintain and install
• Surface skimmer
• Three filtration stages, including a sponge

Cons:

• Noise level is louder than other filters
• Other filters have more filtration stages

20 Gallon Filter FAQ

Do you still have questions about the best 20 gallon filter? Read on to find some common questions and answers.

How Much GPH Does a 20 Gallon Tank Need?

Ideally, you should use a filter with at least 5 GPH per gallon of water. The best 20 gallon filter should have a flow rate of around 100 GPH.

However, there are different factors that influence the ideal flow rate for your tank. The depth of your tank is an important consideration since you’ll want a higher flow rate for a deep tank.

You should also increase the flow rate for a heavily stocked tank since the fish will produce more waste. It’s also best to lower the flow rate if you have a lot of plants since a high flow rate can lower CO₂ levels.

Are Sponge Filters Good for a 20 Gallon Tank?

Sponge filters act as a natural growing medium for beneficial bacteria. They also provide a mechanical filtration step since the fibers of the sponge can trap debris.

However, sponge filters are best for smaller setups. They lack the chemical filtration stage you need when there is a large population of fish producing waste, and they’re not as effective as other mechanical methods of filtration.

Conclusion

We recommend the Aquaclear, Fish Tank Filter as the best 20 gallon filter. This filter delivers multiple stages of filtration and it allows you to adjust the flow rate up to 200 GPH.

It’s one of the best filters for promoting the growth of beneficial bacteria with its porous ceramic rings, and there are additional features for enhancing water quality. Plus, the waterfall design will help add oxygen to your tank.

If you’re willing to spend more, the Aquaeon QuietFlow Canister Filter is another great choice. This filter also delivers a flow rate of 200 GPH and we like that it’s easy to customize the filtration media you use with the nested basket system.