Best Water Filter for a 20 Gallon Aquarium Tank

Carol M.
Fisheries Consultant

As a fish keeper, your aquarium requires proper maintenance and constant upkeep. One of the essential tools required in aquarium maintenance is a water filter. The equipment helps clean your water by eliminating toxic substances that can kill your fish. 

But, how do you find the best water filter? The market is flooded with so many filters,  so it may be tricky to identify the best. This guide will help you find the best water filter for your 20-gallon aquarium. Again, you will learn the importance of using an aquarium water filter and how it works.

Types of Water Filters Best for 20-Gallon Tank

There are various types of filters suitable for a 20-gallon tank. These filters work differently depending on the type of filtration systems applied. Below is a list of different water filters to consider with pros and cons.

  1. Hang On Back (HBO) Filters

The HBO filter is also known as a power filter. The HBO filter is unique and compact equipment. The water gets inside the filter through the lift tube into the chamber. Water gets cleaned inside the enclosed chamber before pumping back to the tank.

This filter works through three biological, chemical, and mechanical systems to clean your aquarium water. The filter contains foam to remove all particulate waste, a ceramic ring for biological filtering, and activated carbon or resins for chemical filtration. 


  • Cost-effective
  • Compact equipment
  • Stand-alone filter for 10-50 gallons tank


  • Requires frequent cleaning replacing once in 3 weeks
  • It's very noisy
  1. Internal and Submersible Filters

The filter can submerge underwater using an electric or air pump. The filter has a case around the suction line that holds filter media like sponges that apply the mechanical filtration system. Again, the filter harbors beneficial bacteria for biological filtering, and some models have a layer of chemical filtering media.

Internal and Submersible Filters
Source: Alamy Stock Photos


  • Saves space
  • Can operate using an air pump or electric


  • It’s hectic to maintain

Under internal filters, we have two types:

  • Box filter – attach to the tank using suckers. It's very affordable.
  • Under gravel filter – has a simple plastic fixed underneath the substrate. It clogs easily thus requires a lot of maintenance.
  1. Canister Filters

The canister is an improved filter best suited for larger tanks, though you can use a smaller model for a 20-gallon tank. The filter offers high-class filtration to your aquarium water, but this comes at a high initial price. The canister features a powerful pump that sucks water into the filter for cleaning.


  • Best filtration technique
  • Require less maintenance
  • Have less noise
  • Flow is adjustable
  • Customizable media options


  • Require critical maintenance
  • Frequent cleaning and replacing once in three weeks
  1. Sponge Filters

This filter is one of the simplest and uses sponge as filtration media. The filter gets submerged in water and powered by an air pump to clean dirty water. The system works using mechanical and biological filtration. The sponge's large surface area creates a conducive environment for the beneficial bacteria. Also, it contains charcoal or zeolite for chemical filtration.

sponge water filter
Source: Alamy Stock Photos


  • Simple in design
  • Low operating costs
  • Gentle water flow
  • It’s cheap


  • Require regular water changes
  • Weak mechanical filtration

Factors to Consider When Purchasing a Water Filter

When choosing an aquarium filter for a 20 gallon, consider these factors;

  • Size- choose a filter size with at least 80 GPH flow rate or more, where water passes through the filter four times in an hour. A Lower flow rate than this isn't best for a 20-gallon tank. Remember to avoid exposing your fish to excess currents.
  • Maintenance – choose a filter that requires less maintenance.
  • Priming – consider a self-priming filter to prevent the motor from burning out and ensuring it works well.
  • Type of Fish- fast-moving fish can handle power currents, but you need less powerful currents and gentle filtration for slow-swimmers.

Top 5 Filter to Consider for 20-Gallon Tank

 These are some of the best water filters you can consider for your tank.

1) AquaClear Hagen (HBO) Filter

AquaClear provides efficient mechanical, biological, and chemical filtrations. It features foam, activated carbon, bio max, and cycle guard for efficient filtration. The filter is known to cause no problems while operating; thus the best choice you can have.


  • It's very quiet
  • Easy to clean and maintain
  • Reliable and durable
  • Well priced and have value for money
  • Easy installation


  • Flow rate can vary, especially if the impeller is dirty
  • Filter bags are a bit expensive though you can use your media mix

2) GRECH CBG-800 (HBO) Filter

The filter comes with a 5 W UV sterilizer to remove bacteria and algae. The filter works through the biological and mechanical filtration system. It's suitable for freshwater and saltwater aquariums as a hang-on back (HBO). The UV sterilizer keeps the water crystal clear while the surface skimmer eliminates all the undesired surface films. Again, the carbon media will help eliminate foul odors from your tank.


  • Easy to regulate water flow
  • Eliminates algae and bacteria in your water
  • Best for a clean and clear aquarium
  • Useful surface skimmer
  • Adjustable flow
  • Silent operation


  • Media basket design is too tight
  • Low-quality carbon media

3) Fluval C Power Filter

This filter is ideal for a 20-gallon tank with an elaborate 5-stage filtration system. The first two stages undergo mechanical filtration, the third chemical, and the last two stages biological process. This process shows the high-efficiency level in getting rid of impurities in your aquarium. The filter operates very fast and can run 153 gallons of water every hour, meaning it will filter water in your tank around seven times.


  • High flow rate
  • It has a fantastic re-filtration system for low flow rates
  • It’s extremely efficient
  • The media is durable and easy to replace
  • 5-stage filtration system for super clean water


  • It's deafening
  • It’s not ideal for larger tanks

4) Fluval Underwater Filter (Internal)

The filter can work even in a 65-gallon tank. It also offers a 3-stage filtration using mechanical, biological, and chemical filtration processes. You can install the filter horizontally for small tanks or vertically to create currents and flow patterns. For better oxygen circulation, it’s best to set it at Top Output.


  • Has 3-way flow control
  • Best for freshwater and saltwater
  • Easy filter replacement
  • Multi-stage filtration


  • Small media basket

5) Marineland Penguin Power Filter( HBO)

This filter is a three-stage mechanical, chemical, and biological filtration system. The filter is unique and has the filter media incorporated in little cartridges, thus making maintenance easy. Cartridges come with filters; thus no need to buy separately. Its filter media is of high quality with the best water quality results.


  • Easy to operate and change media
  • Has replaceable cartridges
  • Easy to mount
  • It's efficient
  • Has features to prevent overheating


  • Unable to prime
  • Costly replacement cartridges

Benefits of Aquarium Water Filter

A water filter is necessary to keep your tank clean and maintain quality water for your fish. Therefore, it’s necessary to purchase a quality filter to reap the best results as follows:

  1. Regulates Water Quality

A water filter helps remove all the toxic waste products in the water and creates a healthy environment for your fish. Accumulation of waste compounds and other substances can be toxic to your fish, causing death. A filter has a biological filtration system that converts toxic ammonia compounds into less toxic nitrate compounds through the nitrogen cycle.

  1. Aerates Water

The living creatures in your aquarium, like fish, require oxygen to survive. Even with water plants that expire oxygen through photosynthesis, this won’t be enough for your fish to survive. A filter comes in handy through the mechanical system by providing extra oxygen. The powerful system agitates the water surfaces and pushes air bubbles into the water.

  1. Maintains the Tank

A filter cleans all the dirt in the water. It removes all the particulate matter that may attach to the substrate or the tank creating an awful smell. Cleaning your aquarium becomes easy if you have an efficient filter.


We hope this article helps find the best filter for your 20-gallon tank. From the five best filters listed above, you should find one that fits your aquarium needs and preferences. Again, we have given you tips to guide you to acquire the best water filter.

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