10 Best Filters for 20-Gallon Aquariums

best filter 20 gallon aquarium

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Selecting the right filter for a 20-gallon aquarium is crucial for maintaining a healthy environment for aquatic life. The top 10 filters, designed specifically for such capacities, ensure optimal water clarity, effective toxin removal, and balanced water flow. These choices cater to various needs, from easy maintenance to silent operation.

What are the Benefits of Aquarium Filters?

Aquarium filters play a pivotal role in sustaining a healthy aquatic environment. Their primary function is to maintain water quality by filtering out impurities, debris, and excess food particles. Simultaneously, they play a vital role in the removal of harmful toxins and waste products produced by aquatic organisms.

These waste products, if left unchecked, can amass to dangerous levels, jeopardizing the health of the tank’s inhabitants. Moreover, filters aid in oxygenating the water, ensuring that aquatic life has a steady supply of oxygen.

Aquarium filters create a clean, stable, and oxygen-rich habitat, mimicking the natural conditions fish would experience in the wild.

Quick List of the Best Filters for 20-Gallon Aquariums

Preview Filter Name  
1. AquaClear Power Filter
2. GRECH CBG-800 Aquarium Filter
3. Fluval C Power Filter
4. Fluval U3 Underwater Filter
5. MarineLand Magnum Canister Filter
6. Aqueon Quietflow Internal Power Filter
7. Fluval 106 External Filter
8. Penn Plax Cascade 700 Canister Filter
9. Aqueon QuietFlow 200 Canister Filter
10. Polar Aurora External Aquarium Filter

Types of Filters Suitable for a 20-gallon Aquarium

For a 20-gallon aquarium, several filter types are ideal. Hang-on-Back (HOB) filters are externally mounted, offering easy maintenance with adequate filtration. Internal filters, placed inside the tank, provide direct filtration and are often quiet. Canister filters, though larger, deliver powerful filtration suitable for tanks with high bioloads. Each type presents unique advantages and considerations, tailored to different needs and tank setups, ensuring optimal water quality and health for aquatic life.

Hang-on-Back Filter (HOB)

The Hang-on-Back (HOB) filter is a popular aquarium filtration system that, as the name suggests, hangs on the rear side of the tank. Featuring a compact design, the HOB pulls water from the tank, processes it through filter media, and then returns the cleaned water back.

HOB filters are easy to install, simple to maintain, and efficient at surface skimming. However, they can sometimes be noisier than internal filters and may not be as powerful as canister types. Ideal for aquarium hobbyists seeking a balance between performance and convenience, HOB filters are especially suitable for medium-sized tanks and those with limited space underneath.

Internal Filter

An Internal Filter is a filtration system designed to operate submerged within the aquarium. Encased typically in a sleek design, it draws water, runs it through filter media, and then disperses the purified water within the tank. One of the primary advantages of internal filters is their quiet operation due to being submerged.

They also save space outside the tank and can be easily hidden behind decor. On the downside, they occupy internal tank space and may require more frequent cleaning. These filters are ideally suited for smaller tanks, aquarists who prioritize aesthetics, and setups where external connections might be challenging.

Canister Filter

A Canister Filter is an external filtration system renowned for its robust performance. Positioned outside the aquarium, it employs a sealed canister to house various filter media layers. Its significant advantages include a high filtration capacity, versatility in media choices, and extended maintenance intervals.

However, canister filters can be more cumbersome to clean and are often pricier than other types. Due to their powerful filtration capabilities, they’re ideal for larger tanks, heavily stocked aquariums, and setups demanding specialized media. Their external nature also ensures no reduction in the tank’s aesthetic appeal or internal space.

What Factors to Consider When Choosing a Filter for a 20-Gallon Aquarium?

When selecting a filter for a 20-gallon aquarium, multiple factors come into play. The capacity and flow rate of the filter is pivotal. The filter should cycle the tank’s water several times an hour, ensuring comprehensive cleaning.

Equally important is the ease of maintenance and cleaning, as regular upkeep is crucial for optimal function. Noise level can impact the tranquility of the setting, so a quieter filter may be preferred, especially in serene spaces.

Budget considerations inevitably shape choices; while investing in quality is wise, options should align with one’s financial boundaries. Also considering specific needs, like the requirements of planted tanks or particular fish species, must guide the final decision, ensuring both flora and fauna thrive.

Reviews of the Best Filters for 20-Gallon Aquariums

The following reviews of the best filters for 20-gallon aquariums provide insights into top-performing filtration systems. These evaluations delve into the features, efficiency, and longevity of various models. By analyzing user feedback and technical specifications, I’ve compiled a comprehensive guide for aquarists. These reviews ensure that individuals can select filters that align with their specific needs, ensuring optimal water quality and a thriving aquatic environment.

1. Aqua Clear Power Filter

The Aqua Clear Power Filter stands as a top-tier choice for aquarium enthusiasts, especially for those with a 20-gallon aquarium. One of its distinctive features is its exceptional contact time with filter media. Coupled with an energy-efficient pump, users can anticipate lower operating costs. Moreover, setting up this filter is a breeze. However, for optimum performance and efficiency, routine maintenance is crucial; it’s recommended to clean the filter bi-weekly.

The Aqua Clear provides three-fold filtration: mechanical, chemical, and biological. Its package incorporates the AquaClear Foam, Activated Carbon Filter, and BioMax, all backed by Cycle Guard for unparalleled water quality. Notably, its filtration volume surpasses its competitors by up to seven times.

Its design concept is rooted in a bottom-up approach, ensuring comprehensive water filtration akin to the functionality of canister filters. The spacious filter chamber is worth noting; it provides room for personal customization of filter media if one desires. One of its patented features is the re-filtration system. This allows users to modulate the flow rate while maintaining a filtration efficiency of up to 50% for the chamber’s water content multiple times.


  • Silent operation ensures minimal disturbance.
  • Provides an avenue to personalize the filtration media.
  • Offers both mechanical and biochemical filtration.
  • Comes with an adjustable flow rate to suit different needs.
  • Installation is user-friendly and quick.


  • The proprietary AquaClear filter media bags have a steeper price, although there’s flexibility in using a personal media mix.
  • The propeller box demands regular maintenance to prevent debris accumulation.


2. GRECH CBG-800 HOB Filter

The GRECH CBG-800 HOB Filter is an adept filtration system tailor-made for aquariums ranging between 20 to 50 gallons. Flaunting dimensions of 9 x 5 x 7 inches, this filter system sports an adjustable flow rate of 211 gph, ensuring optimal water flow based on specific aquarium needs.

What sets the CBG-800 apart is its incorporation of a 5W UV Sterilizer. This feature plays a pivotal role in thwarting algae growth and exterminating harmful bacteria, making the water pristine. Notably, this sterilizer operates independently, granting users the liberty to toggle it on or off as per their needs.

Another remarkable facet is its ‘Hang-On Back’ design, compatible with both freshwater and saltwater ecosystems. This ensures the filter isn’t just functional, but also user-friendly, providing ease during installation and everyday usage. Additionally, it promises a hushed operation, sparing users from incessant noise.

In terms of filtration, the CBG-800 doesn’t disappoint. It offers dual mechanical and biological filtration, equipped with active carbon and bio media. This ensures thorough cleansing of the aquarium environment. A surface skimmer supplements this system, adeptly removing unwanted surface films.

However, like all systems, it’s not without its flaws.


  • Integrated UV sterilizer offers protection against harmful algae and bacteria.
  • Adjustable flow rate, ensuring silent operation.
  • Simplified installation process without the need for additional tools.
  • Surface skimmer for efficient removal of surface films.
  • Comprehensive multi-stage filtration guarantees a crystal-clear aquarium environment.


  • The media basket’s design is somewhat constricted.
  • The provided carbon filter isn’t of the highest quality, possibly necessitating a personal replacement.


3. Fluval C Power Filter

The Fluval C Power Filter, crafted by the renowned brand Fluval, is a state-of-the-art HOB (Hang-On Back) filtration system tailored for both freshwater and saltwater aquariums ranging from 20 to 50 gallons. What sets this filter apart is its impressive 5-stage filtration system, ensuring a thorough and comprehensive cleaning process.

  1. Polyfoam media captures both large and fine debris. This is easily replaceable every 4-6 weeks.
  2. Biological C-nodes enhance the biological filtration and are replaceable semi-annually. However, only 50% should be replaced at once to maintain consistent biological activity.
  3. Activated carbon media handles the chemical stage, efficiently removing toxins. This needs replacement every 2-4 weeks.
  4. Bioscreen functions in the biological stage, obstructing debris and offering a vast surface area for beneficial biological activities. It requires replacement every 2-3 months.
  5. The filter also incorporates a Motor o-ring that needs annual replacement.

A noteworthy feature of the Fluval C3 filter is its modular media compartment. This design not only facilitates easy cleaning of each compartment independently but also allows users to customize their filter media mix.

Additionally, the filter’s adjustable flow rate feature provides users the liberty to tailor the flow based on their aquarium needs without compromising on its efficiency.


  • Boasts a robust 5-stage filtration process.
  • Easy installation with straightforward assembly and disassembly.
  • Offers the flexibility to use a personalized filter media mix.
  • Features an adjustable water flow system.


  • Cleaning the impeller can be a bit challenging.
  • The spout, which drips water onto the bio-media, is susceptible to clogging.
  • Different replacement dates for each filter stage can be hard to track.


4. Fluval U3 Underwater Filter

The Fluval U3 Underwater Filter, a brainchild of the renowned brand Fluval, stands out as an integral piece of aquarium equipment designed for versatility. Sized at 12″ L x 6″ W x 5″ H and weighing a mere 1.76 pounds, it seamlessly blends into aquariums without causing an obtrusion.

Designed for aquariums up to 40 gallons, this filter serves either as the primary filtration system for smaller setups or an auxiliary one for larger tanks. Its innovative design showcases a sleek structure equipped with an easy-grip water control panel and a newly conceptualized media cartridge ensuring efficient debris capture.

Among its prime features is the convenient flip-top lid, designed for effortless access during maintenance or cartridge replacements. Furthermore, users are bestowed with the flexibility of positioning this filter horizontally – perfect for shallow tanks or decorative waterfall creations, or vertically – ideal for inducing specific water currents or flow patterns. This adaptability makes the U3 model particularly suited for freshwater, marine, or even reptile environments.

The Fluval U3 encompasses a comprehensive 3-stage filtration system: mechanical, chemical, and biological, ensuring optimal water quality. The device also incorporates the unique Adjustable 3-Way Flow Control, allowing users to calibrate the water flow according to the tank’s specific requirements.


  • Offers robust multi-stage filtration.
  • Innovative 3-way flow control feature.
  • Versatile installation options, both vertically and horizontally.
  • Suitable for a wide range of environments: freshwater, marine, and reptilian.
  • Designed for tanks sized 20-40 gallons.


  • The media compartment might feel slightly cramped.
  • For a 40-gallon tank, the U3 model might be slightly underpowered, suggesting that the U4 model might be a more fitting choice.


5. MarineLand Magnum Polishing Internal Canister Filter

From the reputable brand MarineLand comes the Magnum Polishing Internal Canister Filter, a tool designed to ensure the highest quality of water for aquatic life. Weighing in at 3 pounds, this internal canister filter stands out due to its robust and efficient filtration capabilities.

Central to its functionality are the two refillable chambers, which house either activated carbon or customizable filter media. This level of adaptability makes the MarineLand Magnum one of the most versatile filters available. With a submerged motor, the start-up process is both quick and seamless, eliminating the hassle of manual priming. Capable of processing a whopping 290 gallons of water per hour, this filter serves as an ideal choice for aquariums scaling up to 97 gallons.

Diving deeper into its features, it offers a comprehensive three-stage filtration:

  1. Mechanical Filtration – Here, the Rite-Size floss sleeve adeptly captures dirt and debris.
  2. Chemical Filtration – The Black Diamond Premium Activated Carbon ensures the elimination of water impurities, discoloration, and odors.
  3. Biological Filtration – A dual-chamber design enhances biological activity, neutralizing harmful substances like ammonia and nitrites through the action of beneficial bacteria.

Additionally, the filter boasts an effective water polishing mechanism using a reusable pleated micron cartridge, ensuring the water remains crystal clear.


  • Immense filtration capacity, processing up to 290 gallons/hour.
  • Tailored for sizable aquariums.
  • Provides a trifecta of filtration methods.
  • The dual-chamber design allows for media customization.
  • Maintenance made easy with its design and self-priming feature.


  • Given its size, it occupies a significant space within the aquarium.
  • Operational noise can be relatively louder.
  • Optimal for larger aquariums, specifically those exceeding 50 gallons.


6. Aqueon Quietflow Internal Power Filter

The Aqueon QuietFlow Internal Power Filter is a premium-grade filtration system designed for both aquariums and terrariums. As the name suggests, one of its standout features is its quiet operation, ensuring minimal disturbance in your living space.

Diving into its functionalities, this filter is engineered to offer a comprehensive three-stage filtration process, ensuring pristine water quality for aquatic inhabitants. This includes:

  1. Mechanical Filtration – A dense foam effectively captures and removes debris and particulate matter from the water.
  2. Chemical Filtration – The activated carbon layer efficiently neutralizes toxins, combats odors, and clarifies water by eliminating discoloration.
  3. Biological Filtration – The patented BioGrid plays a crucial role in mitigating harmful substances like ammonia and nitrates, promoting a healthier aquatic environment.

A unique feature of the Aqueon QuietFlow is its adaptability. The filter can be fully submerged and installed either vertically or horizontally, depending on the user’s preference. Additionally, it boasts an adjustable return flow rate, allowing for a tailored water flow that best suits your aquatic setup.

Ease of maintenance is another commendable attribute. The filter employs specially designed Aqueon replaceable cartridges, making the replacement process straightforward and hassle-free.


  • Operates silently, ensuring minimal disturbance.
  • Provides an all-encompassing 3-stage filtration mechanism.
  • Cartridge replacement is a breeze.
  • Versatility in installation, be it vertical or horizontal.


  • The unit’s design can be somewhat bulky, occupying a noticeable space within the aquarium.
  • The smallest size variant of the filter might not offer the full spectrum of mechanical and biological filtration, potentially limiting its efficacy for some setups.


7. Fluval 106 External Filter

The Fluval 106 External Filter is a state-of-the-art filtration system tailored for both freshwater and saltwater aquariums. With its modern black design and cylindrical shape, this filter, produced by the renowned brand Fluval, seamlessly integrates aesthetics and functionality.

This canister filter is specifically engineered for tanks up to 25 gallons. One of its remarkable attributes is the multi-stage filtration system. The filtration process begins with twin foam pre-filters that efficiently capture debris, safeguarding other media from clogging. Following this, there are two other stages encompassing chemical and biological filters which ensure comprehensive water purification. This modular system facilitates easy access and changeover of the filter media, streamlining maintenance processes.

A distinguishing feature of the Fluval 106 is the patented AquaStop Valves. These valves are meticulously designed to halt water flow without any leakage, negating the need for disconnecting hoses, thus ensuring a mess-free experience. Additionally, the filter boasts a sound-dampening impeller, ensuring a quieter ambiance, which is a boon for many aquarists.

Despite its powerful functionalities, the Fluval 106 also prioritizes user convenience. With features like instant priming, the tedious task of manual siphoning is entirely eliminated.


  • Effortless maintenance due to its user-friendly design.
  • Comprehensive multi-stage filtration system.
  • AquaStop Valves facilitate leak-free water flow interruptions.
  • Instant priming feature eliminates the need for manual siphoning.


  • The filter’s powerful flow might necessitate the addition of a spray bar for those seeking a lower flow setting.
  • Some users have reported impeller issues within 6-12 months. However, it’s worth noting that a 3-year warranty backs the product, attesting to its quality and durability.


8. Penn Plax Cascade 700 Canister Aquarium Filter

The Penn-Plax Cascade 700 Aquarium Canister Filter stands out as a sophisticated tool for maintaining pristine water quality in aquariums. Recommended for tanks up to 65 gallons, it boasts an impressive water cycling rate of 185 gallons per hour.

Equipped with state-of-the-art features, the Cascade 700 ensures efficient and silent operation. One notable feature is its push-button primer, making the start-up process effortless. For added convenience, the filter includes swimming-pool style hose clamps, making installation quick and hassle-free. Furthermore, the two independent valve taps are capable of a 360° rotation, providing flexibility even in cramped spaces like tight aquarium cabinets.

Ensuring a healthy aquatic environment is paramount. With that in mind, the Cascade 700 comes pre-loaded with essential filter media. This includes 2 poly fiber floss pads, a coarse bio-sponge, and a bag of activated carbon. Such a combination guarantees physical, biological, and chemical filtration, ensuring the removal of waste, excess food, and other impurities.

While designed predominantly for fish tanks, both freshwater and saltwater, its versatile functionality extends to turtle habitats as well.


  • Offers multi-stage filtration, ensuring comprehensive water purification.
  • Simple and quick setup due to the push-button primer and included filter media.
  • The adjustable flow rate caters to various aquatic needs.
  • Boasts a robust, tip-proof design ensuring stability.


  • Some users have encountered difficulties with connecting the tubes.
  • Occasional priming issues have been reported, although they seem to be isolated incidents.


9. Aqueon QuietFlow 200 Canister Filter

For aquarists seeking efficient water filtration, the Aqueon QuietFlow 200 Canister Filter is a notable contender. With a liquid volume capacity of 55 gallons and weighing in at 12.4 pounds, this filter is designed primarily for fish tanks.

At the heart of this filter is its multi-stage filtration system. Users get a comprehensive package that includes activated carbon, coarse foam, bio-balls, bio-ceramic rings, and a water polishing unit with a cartridge. This assortment ensures a holistic purification approach, catering to mechanical, chemical, and biological filtration needs. Furthermore, the filter comes equipped with essential features like quick disconnect valves, pump locking heads, and water intake/output connections. These features make maintenance and cleaning less cumbersome.

User reviews present a mixed bag of experiences. Many appreciate its silent operation, efficiency, and adaptability, particularly praising its easy-access design for routine maintenance. Some have lauded its affordability, especially considering its canister filter category. However, challenges arise during its cleaning phase. Users have cited time-consuming cleaning processes and difficulty in handling the hoses. Furthermore, concerns about reduced flow and limited adjustment flexibility on intake have been highlighted.

Based on user feedback, here’s a concise breakdown:


  • Quiet operation ensuring minimal disturbance.
  • Effective multi-stage filtration.
  • Adaptable design that can be tweaked for specific needs.
  • Affordable, offering good value for money.


  • Cleaning can be time-consuming, especially concerning hose lines.
  • Some users faced challenges with flow rate adjustment and limited intake flexibility.
  • A few concerns about odor from the tubing were reported.


10. Polar Aurora Free Media External Aquarium Filter

Polar Aurora’s Canister Filter is a robust filtration system that serves aquariums up to 75 gallons. This filter, capable of a flow rate of 264 GPH (1000L/hr) driven by an 18W pump, introduces several features to facilitate its usage. It offers three media trays that can be filled with one’s choice of filtration media, whether that’s SunSun’s activated carbons, ceramic rings, or bio-balls. This ensures mechanical, chemical, and biological filtration for crystal-clear water.

The filter boasts an adjustable spray bar, enabling users to control the output flow, and a convenient self-priming pump, which eradicates the need for manual siphoning. Moreover, the single valve disconnect and priming pump simplify routine maintenance tasks. An important thing to note is that the manufacturer conducts water pressurize tests before packaging to ensure no leaks, so any condensation within is merely trapped moisture.

However, despite these features, user feedback paints a varied picture:


  • Large capacity suitable for up to 75-gallon tanks.
  • Versatile with three customizable media trays.
  • Easy-to-use adjustable spray bar.
  • Self-priming pump removes the need for manual siphoning.
  • Positive reviews on its quiet operation.
  • UV sterilizer with an external switch for added convenience.
  • Competitive pricing offering good value.


  • Some users found the hoses hard to flex and manipulate.
  • Concerns about the durability and quality of certain parts, such as the plastic accessories.
  • Some reported issues with the priming function.
  • Few users encountered leaking problems.
  • Limited lifespan with some reporting problems post a 2-year mark.
  • Inconsistent customer service experiences.

User feedback has also highlighted the need for potential modifications and enhancements, such as the usage of plumbers tape to prevent leaks. While many applaud the filter for its efficacy, especially at its price point, others believe it’s a temporary solution before upgrading to a higher-end product.

What are the Best Ways to Use and Maintain Aquarium Filters?

Using and maintaining aquarium filters efficiently is paramount for a thriving aquatic environment. Regular maintenance, including cleaning and replacing filter media, is crucial to prevent toxin buildup and ensure consistent water quality. In certain setups, combining different filter types can optimize filtration, catering to specific needs more effectively.

Additionally, overstocking should be avoided, as it burdens the filtration system and deteriorates water quality. Furthermore, adjusting the flow rate is essential; swift currents might distress certain fish, while some plants flourish with gentle flows.

What are the Benefits of Using a Filter for a 20-Gallon Guppy Tank?

A filter for a 20-gallon guppy tank enhances water quality by removing impurities, waste, and toxins. It provides essential biological filtration, promoting beneficial bacteria growth that converts harmful ammonia and nitrites. A filter ensures consistent water circulation, preventing stagnant zones and promoting oxygenation. For guppies, this results in a healthier environment, leading to vibrant colors, active behaviors, and a lower risk of disease outbreaks.

What Are the Benefits and Downsides of Internal vs. External Filters for 20-Gallon Tanks?

Internal and external filters serve the primary function of cleaning and purifying water in a 20-gallon tank. Internal filters, situated inside the tank, are typically easier to install and are ideal for smaller tanks due to their compact design. They ensure effective water circulation but might occupy significant space and can sometimes be seen as an eyesore.

External filters, on the other hand, are located outside the tank. They are generally more powerful and suitable for larger tanks or those with numerous inhabitants. However, they can be bulkier, often more expensive, and may require more complex setups and maintenance compared to their internal counterparts.

What Are the Benefits and Downsides of Internal vs. HOB Filters for 20-Gallon Tanks?

Internal filters, placed inside 20-gallon tanks, offer easy installation and direct water circulation but can occupy valuable space and disrupt aesthetics. Hang-On-Back (HOB) filters, attached to the tank’s rim, provide powerful filtration and are less intrusive visually.

However, they can be noisier and require more frequent maintenance. Both filters effectively purify water, but the choice between them hinges on personal preference, tank setup, and maintenance willingness.

Why are Sponge Filters Not Suitable for 20-Gallon Tanks?

Sponge filters are favored for their simplicity and biological filtration capabilities. However, for 20-gallon tanks, they might not be the most efficient choice. Their filtration capacity can be limited for larger volumes of water, leading to insufficient removal of impurities.

Additionally, they lack the comprehensive mechanical and chemical filtration often necessary for tanks of this size. Thus, relying solely on a sponge filter for a 20-gallon tank may compromise water clarity and quality.

What is the Required Filter Capacity for 20-Gallon Aquariums?

For a 20-gallon aquarium, the ideal filter capacity should circulate the tank’s entire volume at least 3-4 times per hour, translating to 60-80 gallons per hour (GPH). This ensures adequate water turnover, helping to maintain optimal water quality.

What are the Benefits of Using Two Filters in a 20-Gallon Fish Tank?

Using two filters in a 20-gallon fish tank offers enhanced reliability; if one fails, the other provides backup. This dual-setup promotes more uniform water circulation, ensuring no “dead spots” with stagnant water. Additionally, it supports better mechanical, chemical, and biological filtration, leading to clearer, cleaner water. Two filters can also ease the burden on each unit, potentially extending their lifespans and allowing for more flexible maintenance schedules.

Updated: October 5, 2023
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