Best External Aquarium Filters 2025

Importance of Filtration in Aquatic Life

When we think about keeping fish, we often focus on the tank size, the type of fish, and the decor. However, one crucial element that can’t be overlooked is filtration. An external aquarium filter plays a vital role in maintaining a healthy environment for your aquatic life. It works by circulating water through various filtration media, removing harmful toxins, debris, and excess nutrients that can build up in the tank. Without proper filtration, harmful substances such as ammonia and nitrites can accumulate, leading to stress or even death in fish. An external aquarium filter not only cleans the water but also helps in maintaining stable water parameters, which is essential for the wellbeing of your fish.

How External Filters Work

External filters function by drawing water from the aquarium, filtering it through different media, and returning the clean water back to the tank. Typically, they consist of three main stages of filtration: mechanical, chemical, and biological. Mechanical filtration captures visible particles like uneaten food and fish waste. Chemical filtration removes toxins and discoloration through media like activated carbon. Biological filtration supports beneficial bacteria that break down harmful substances, creating a balanced ecosystem in your tank. This multi-faceted approach ensures that your aquarium remains clean and your fish thrive.

Flow Rate Matters

When selecting an external aquarium filter, one of the most important specifications to consider is the flow rate. This is the amount of water that the filter can process in a given time, usually measured in litres per hour. Ideally, the filter’s flow rate should be capable of filtering the entire volume of your tank at least once every hour. For example, if you have a 100-litre tank, choose a filter with a flow rate of at least 100 litres per hour. This ensures efficient filtration and creates a suitable environment for your fish.

Filtration Media Options

Another feature to pay attention to is the type of filtration media the filter supports. Having the flexibility to use various media types allows for customisation based on the needs of your aquarium. Some filters come with pre-installed media, while others allow you to choose what you want to use. Look for filters that accommodate different media such as sponge, ceramic rings, and activated carbon, giving you the ability to tweak your filtration according to the specific needs of your tank.

Ease of Maintenance

Ease of maintenance is crucial for maintaining a clean aquarium. Consider how easy it is to access the filter components and replace or clean the media. Some filters offer features like a quick-release mechanism for hassle-free cleaning, which will save you time and effort. Additionally, a filter with a transparent body can help you monitor the state of the filtration media at a glance, allowing you to know when it’s time for a change.

Noise Level

While function is key, we also want our filtration systems to run quietly, especially if the aquarium is in a living space. Look for external filters that are advertised as ‘quiet operation’ or have sound-dampening features. This is particularly important in smaller spaces where the sound might be more noticeable. A quiet filter enhances your overall aquarium experience, allowing you to enjoy the visual appeal of your tank without the distraction of unwanted noise.

Gather Your Materials

Before you begin the setup, ensure you have all the necessary materials. You’ll need the external filter, the associated tubing, and the filtration media specified in the user manual. It’s a good practice to lay everything out beforehand to ensure a smooth installation process.

Positioning the Filter

Choose a suitable location for the filter. It should ideally be placed below the aquarium level, allowing gravity to facilitate water flow. Ensure the position is stable and secure to prevent any accidental falls or leaks. Once you have found an appropriate spot, fix the filter in place.

Connecting the Tubing

Next, connect the tubing according to the instructions provided. The inlet will draw water from the tank into the filter, while the outlet will return the filtered water back. Make sure the tubing is securely attached and free of kinks that could interfere with the water flow. Ensure that both inlet and outlet tubes are positioned correctly in the tank for optimal circulation.

Filling the Filter with Water

Before turning on the filter, fill it with water to prevent it from running dry during its initial start-up. This can be done by either pouring water into the filter or using the outlet tube to siphon water from the tank.

Plugging in and Testing

Finally, plug the filter into the power outlet and start the operation. Check for any leaks around the tubing connections and ensure the flow rate is as expected. It’s advisable to keep an eye on the aquarium environment for the first few hours to ensure everything is functioning correctly.

Regular Cleaning Schedule

To ensure your external filter operates efficiently, it’s important to establish a regular cleaning schedule. Depending on your tank’s bioload—how many fish and how much feeding you do—this may need to occur every 4 to 6 weeks. During maintenance, turn off the filter, disconnect the tubing, and follow the manufacturer’s cleaning instructions for the filter components.

Media Replacement Tips

Filtration media should also be replaced or refreshed periodically. Mechanical filters typically require more frequent cleaning or replacement, while biological media usually only needs to be rinsed in tank water during major cleanings to preserve your beneficial bacteria. Always follow the guidelines for each media type to maintain an effective filtration system.

Check for Wear and Tear

Make it a habit to check the filter and its components for signs of wear and tear regularly. Look out for cracks or any blockages that could impede water flow. If the filter makes unusual sounds, this could indicate potential issues that need to be addressed. Early detection can help prevent more significant problems down the line.

AquaClear External Filter

The AquaClear External Filter is a great all-rounder for aquarists. It features adjustable flow rates, allowing you to customise the filter speed based on your specific tank requirements. It also accommodates various filter media and provides excellent mechanical, chemical, and biological filtration, making it an ideal choice for both beginner and experienced fish keepers.

Fluval 406 External Filter

For larger tanks, we recommend the Fluval 406 External Filter. It boasts a high flow rate and innovative multi-stage filtration system, ensuring crystal clear water. Additionally, its quiet operation makes it perfect for homes where noise can be an issue. It’s equipped with a self-priming feature, simplifying the setup and maintenance process.

Eheim Classic External Filter

The Eheim Classic External Filter is known for its reliability and longevity. It’s a simple design but effective, offering efficiency in a compact package. With a wide range of sizes available, it can cater to various tank sizes while providing robust filtration capabilities, making it suitable for a wide array of aquatic environments.