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Choosing the Best Aquarium Filter

Choosing the best aquarium filter, Image of aquarium filters

The Ultimate Guide to Choosing the Best Aquarium Filter

As you probably already know, setting up a new aquarium can be both exciting and challenging, and one of the most important choices you will have to make is selecting the best aquarium filter. With so many options available, it can be a bit overwhelming, but don’t worry — whether you are new to the hobby, a seasoned veteran, or maybe someone looking for the best products for your fish tank, this guide will help you understand the difference between each type of filter, how they work, and which one might be the best fit for your needs.

Table of Contents

How Do Aquarium Filters Help?

Aquarium filters are essential for keeping your tank healthy. They do three main things:

  • Mechanical Filtration: This helps remove debris like uneaten food, fish waste, and dead plant matter from the water. Without a filter, these particles would make your water cloudy and could harm your fish.
  • Biological Filtration: Beneficial bacteria live on filter media and convert toxic ammonia and nitrites into less harmful nitrates, which helps keep your water safe for your fish.
  • Chemical Filtration: Some filters use activated carbon or other chemical media to remove impurities like chlorine, dissolved organic compounds, and odors from the water.

Without a good filter, the water in your tank can quickly become toxic, leading to stress, illness, or even death for your fish. Whether you’re just starting out or you’ve been keeping aquariums for years, choosing the right filter is key to maintaining a healthy environment.

There are several types of aquarium filters, each with its own strengths and weaknesses. The best choice for you will depend on your tank size, the type of fish and plants you have, your budget, and how much time you’re willing to spend on maintenance.


Image of sponge filters

Sponge Filters

Purpose: Sponge filters are one of the simplest types of filters. They use an air pump to draw water through a sponge, providing both mechanical and biological filtration.

How It Works: The sponge traps debris as water flows through it, and beneficial bacteria grow on the sponge’s surface, breaking down ammonia and nitrites. The air pump also helps oxygenate the water.

  • Pros:
    • Low cost: Sponge filters are among the cheapest options, making them great for anyone on a budget.
    • Gentle water flow: They’re ideal for delicate species like shrimp, fry, and small fish that can’t handle strong currents.
    • Effective biological filtration: The sponge becomes a home for beneficial bacteria, helping to maintain a healthy nitrogen cycle.
    • Easy to clean: Just squeeze the sponge out in a bucket of tank water during water changes to clean it.
  • Cons:
    • Limited mechanical filtration: While the sponge can catch large particles, it doesn’t do as well with finer debris.
    • Not ideal for larger or heavily stocked tanks: The filtration capacity is limited, so they’re better for smaller tanks (under 30 gallons) or as a secondary filter.
  • Best Use Cases: Sponge filters are great for small tanks or breeding setups where gentle filtration is important. They’re also perfect for shrimp tanks, where the gentle flow won’t harm delicate invertebrates.

If you’re looking for a reliable sponge filter, check out these. I use at least two in all my tanks:



Image of an HOB filter

Hang-On-Back (HOB) Filters

Purpose: HOB filters are extremely popular, especially among beginners. These filters hang on the back of the tank and provide mechanical, biological, and chemical filtration.

How It Works: Water is drawn up from the tank through an intake tube, passed through various types of filtration media, and then returned to the tank.

  • Pros:
    • Easy to use: HOB filters are simple to install and maintain, making them a great choice for beginners.
    • Versatile: You can customize the filter media to suit your tank’s needs.
    • Effective: They offer a good balance of mechanical, biological, and chemical filtration, making them suitable for a wide range of setups.
    • Moderate cost: These filters are affordable and come in various sizes to fit different tanks.
  • Cons:
    • Visible in the tank: Since they hang on the back, the intake and outflow tubes are visible, which some aquarists might not like.
    • Noise: Some HOB filters can be noisy, especially if the water level drops too low.
    • Frequent media replacement: The carbon or other chemical media in these filters typically needs to be replaced every 4-6 weeks.
  • Best Use Cases: HOB filters are ideal for small to medium-sized tanks, up to about 75 gallons. They’re especially popular in community tanks where multiple species need balanced filtration. They’re also perfect for anyone looking for a low-maintenance option.

If an HOB is the one for you, here are a couple the I really like that are very reasonably priced and reliable:



Image of a canister filter

Canister Filters

Purpose: Canister filters are external units that offer high-efficiency filtration, particularly for larger tanks. They house multiple types of media, providing superior mechanical, biological, and chemical filtration.

How It Works: Water is siphoned from the tank into the canister, where it passes through various stages of filtration. The filtered water is then pumped back into the tank. The media can be customized to meet specific filtration needs.

  • Pros:
    • Excellent filtration: Canister filters are highly effective and can handle large volumes of water, making them ideal for heavily stocked or large tanks (over 50 gallons).
    • Customizable media: You can adjust the filtration to suit your tank’s needs by adding different types of sponges, bio-media, or activated carbon.
    • Quiet operation: Since the motor is outside the tank, these filters are generally quieter than HOB filters.
    • Out of sight: The filter is placed outside the tank, so you don’t have bulky equipment hanging inside your aquarium.
  • Cons:
    • More expensive: Canister filters are generally pricier than HOB or sponge filters.
    • Complex setup: They require more time to set up and maintain, and cleaning them can be more involved, especially for beginners.
    • Large footprint: These filters take up space outside the tank, which could be an issue if you’re short on space.
  • Best Use Cases: Canister filters are the top choice for large tanks, heavily stocked tanks, or setups with large fish that produce a lot of waste. They’re also great for aquarists who want maximum customization and control over their filtration system.

If a canister filter sounds right for you, I’ve had great success with the Fluval ’07 series:



Image of an Undergravel filter

Undergravel Filters

Purpose: Undergravel filters are among the oldest types of aquarium filtration. They sit under the substrate and use the gravel itself as the primary filtration media.

How It Works: Water is drawn down through the gravel, which traps debris and serves as a biological filter. An air pump or powerhead helps circulate water through the gravel and back into the tank.

  • Pros:
    • Inexpensive: These filters are relatively low-cost compared to other types.
    • Encourages beneficial bacteria: The gravel provides a large surface area for beneficial bacteria to grow.
    • Hidden from view: Since the filter is buried under the substrate, it doesn’t interfere with your tank’s appearance.
  • Cons:
    • Hard to maintain: Cleaning an undergravel filter can be challenging because debris builds up in the gravel over time, leading to poor water quality if not properly maintained.
    • Limited mechanical filtration: These filters don’t trap fine particles well, so you may need to use another type of filter in conjunction with it.
    • Not ideal for planted tanks: The filtration process can disturb plant roots, making undergravel filters less suitable for tanks with live plants.
  • Best Use Cases: Undergravel filters are best for low-tech, lightly stocked tanks with hardy fish. They’re also a good option for beginners looking for a simple, inexpensive filtration system, as long as they’re prepared to do regular substrate cleaning.

If the undergravel filter is something you’re interested in, here are a couple options:



Image of an internal filter

Internal Filters

Purpose: Internal filters are compact units that sit inside the tank, typically attached to the glass with suction cups. They provide mechanical, chemical, and biological filtration depending on the media used.

How It Works: Water is drawn into the filter, passes through the filtration media, and is then returned to the tank. These filters are fully submersible, making them quiet and unobtrusive.

  • Pros:
    • Compact design: These filters are small and easy to hide behind plants or decorations.
    • Quiet operation: Since they’re submerged, internal filters are generally quieter than HOB filters.
    • Affordable: Internal filters are typically inexpensive, making them a good choice for anyone on a budget.
  • Cons:
    • Limited capacity: They’re best suited for smaller tanks due to their size and capacity.
    • Space inside the tank: Internal filters take up space in the tank, which can be a downside in smaller setups.
    • Frequent maintenance: Depending on the filter media, internal filters may need to be cleaned or replaced more often than other types.
  • Best Use Cases: Internal filters work well in small to medium-sized tanks (up to 40 gallons). They’re a great choice for beginners or for use in breeding or quarantine tanks where reliable but gentle filtration is needed.

If you like the way this filter sounds (which is silent), here are a few great options that are very inexpensive and very easy to manage:


Fluidized Bed Filters (not a wonderful option)

Purpose: Fluidized bed filters use fine sand or other granular media for biological filtration. These filters are known for their high efficiency in processing ammonia and nitrites.

How It Works: Water is pumped through a chamber filled with fine media, which is kept in constant motion (fluidized) by the water flow. This movement maximizes the surface area for beneficial bacteria, making the filter extremely efficient at biological filtration.

  • Pros:
    • Excellent biological filtration: The fluidized bed maximizes the surface area for bacterial colonization, making it very effective at processing ammonia and nitrites.
    • Compact and efficient: These filters are relatively small and can handle a high bio-load despite their size.
    • Low maintenance: Once set up, fluidized bed filters require minimal maintenance compared to other types.
  • Cons:
    • No mechanical or chemical filtration: These filters are purely biological, so you’ll need to use them alongside other filtration methods to ensure your water stays clean.
    • Complex setup: They can be tricky to set up, especially for beginners. You’ll need to balance the flow rate to keep the media fluidized without causing clumping.
    • Not suitable for fine substrates: If you have fine sand or similar substrates, they could get sucked into the filter, causing blockages or reducing efficiency.
  • Best Use Cases: Fluidized bed filters are perfect for heavily stocked tanks or those with large, messy fish like cichlids or goldfish. They’re also great for advanced aquarists looking to add extra biological filtration to their setup. These filters are often used in large or commercial tanks because of their efficiency.

What Should I Consider When Choosing an Aquarium Filter?

Choosing the right aquarium filter isn’t just about picking a brand or model. There are a few key factors you should consider:

Tank Size and Stocking Levels

The size of your tank and the number of fish you keep will greatly affect your filtration needs. Larger tanks with more fish produce more waste and need more powerful filtration. For example:

  • Small Tanks (5-20 gallons): Sponge filters, small internal filters, or HOB filters usually do the trick. These tanks often house small fish, shrimp, or a few plants.
  • Medium Tanks (20-55 gallons): A good HOB or canister filter can handle the increased waste production, making them ideal for community tanks or those with medium-sized fish.
  • Large Tanks (55+ gallons): Canister filters or a combination of multiple filters (e.g., canister plus HOB) are usually necessary. Large tanks may have big, waste-producing fish or be heavily planted, requiring robust filtration.

Maintenance and Ease of Use

Consider how much time and effort you’re willing to put into maintaining your filter:

  • Ease of Cleaning: HOB and sponge filters are relatively easy to clean, with accessible media that can be rinsed or replaced quickly.
  • Frequency of Maintenance: Canister filters, while highly effective, require more time to disassemble and clean. However, they don’t need to be cleaned as often as HOB or internal filters.
  • Replacement Media Costs: Some filters, especially HOB and canister filters, require regular media replacement, such as activated carbon or filter pads. Make sure to factor these costs into your decision.

Budget Considerations

Your budget is also important:

  • Initial Costs: Sponge filters and small internal filters are budget-friendly. HOB filters are a bit more expensive but still within reach for most aquarists.
  • Long-term Costs: Canister filters have higher upfront costs but offer great longevity and efficiency. Consider the cost of replacement media and electricity usage over time.

Noise Levels and Aesthetics

The noise level and appearance of your filter might also influence your decision:

  • Noise: Some filters, like certain HOB models, can be noisy, especially if the water level drops too low. Canister and internal filters are usually quieter.
  • Aesthetics: If you prefer a clean look, consider a filter that’s hidden (like an undergravel or canister filter) or one that’s easy to hide (like a small internal filter). HOB filters are effective but are visible on the back of the tank.

How Do I Maintain an Aquarium Filter?

Regular maintenance is key to keeping your aquarium filter running smoothly. Here’s how to ensure your filter performs its best:

Cleaning Frequency

  • Sponge Filters: These should be cleaned every 2-4 weeks, depending on how many fish you have. Just remove the sponge and rinse it in a bucket of aquarium water to remove debris without killing beneficial bacteria.
  • HOB Filters: Clean the intake tube and filter media monthly. Replace the carbon filter cartridge every 4-6 weeks.
  • Canister Filters: Canister filters need cleaning every 2-3 months. It’s a bit more work, but you’ll need to disassemble the unit and clean each component thoroughly.
  • Undergravel Filters: These require regular gravel vacuuming to prevent debris buildup. Consider doing a deep clean every 6-12 months, which involves lifting the plate and cleaning underneath it.
  • Internal Filters: Clean these every 2-4 weeks. Remove the filter media and rinse it in aquarium water, and wipe down the inside of the filter to prevent algae buildup.
  • Fluidized Bed Filters: These require minimal maintenance, but you should check the flow rate regularly to ensure the media stays properly fluidized.

Replacing Filter Media

Different types of filter media need replacing at different intervals:

  • Activated Carbon: Replace it every 4-6 weeks as it loses effectiveness over time.
  • Sponges: These can last for years if maintained properly, but replace them if they start to break down.
  • Bio-media (e.g., ceramic rings): Bio-media rarely needs replacing since it’s where beneficial bacteria live. Just rinse it occasionally to remove debris.
  • Mechanical Media (e.g., filter pads): Replace these when they become clogged and reduce water flow.

Signs Your Filter Needs Attention

Keep an eye out for these signs that your filter needs cleaning or maintenance:

  • Reduced Water Flow: If water isn’t flowing as strongly as it used to, the filter media may be clogged.
  • Unusual Noises: Rattling, buzzing, or grinding noises can mean the impeller is dirty or something is stuck in the intake tube.
  • Cloudy Water: Persistent cloudiness could indicate your filter isn’t working well, possibly due to clogged media or an insufficient flow rate. Learn more about fixing cloudy water.
  • Foul Odors: If your tank smells bad, it might be time to replace the filter media or clean out accumulated debris in the filter.

Conclusion: Finding the Best Aquarium Filter

Choosing the right aquarium filter is crucial to keeping your tank healthy and your fish happy. By understanding the different types of filters and considering your tank’s size, stocking levels, maintenance preferences, and budget, you can find the filter that’s perfect for your setup.

If you’re still unsure which filter to choose, feel free to leave a comment below or contact us directly for personalized advice. And don’t forget to check out our shop for a selection of top-rated aquarium filters and other supplies to help you create the perfect aquatic habitat.

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