Types of Filters

Hang on Back (HOB) Filters

As the name suggests, Hang-On-Back (HOB) filters are compact units that hang on the side of your tank. They draw water up from the aquarium, push it through a filter cartridge, and return the cleaned water back into the tank. These filters are popular in aquarium kits because of their simplicity, ease of use, and range of available sizes.

While manufacturers often recommend replacing the filter cartridge every month, this suggestion is typically driven by the desire for recurring sales rather than the actual needs of your tank. In reality, replacing the cartridge so frequently isn’t necessary and could actually harm your aquarium. Doing so removes the beneficial bacteria that help maintain your tank’s balance, which can lead to a spike in ammonia and other problems. Instead of replacing the cartridge, simply rinse it in old tank water when it becomes clogged and continue using it until it starts to degrade.

Pros of HOB Filters

Easy to set up and use: HOB filters are straightforward to install and require minimal maintenance.
Affordable: These filters are typically less expensive compared to other filtration options.
Low-maintenance cleaning: Cleaning is hassle-free and requires only occasional rinsing.
Low leak potential: Since the filter hangs on the tank, it generally has a low risk of leaking, making it a reliable choice.

Cons of HOB Filters

Limited surface area for bacteria: The filter’s design provides minimal surface area for beneficial bacteria, which is the primary purpose of a filter. This can be partially alleviated by adding more porous sponge material inside the filter box, allowing for more bacterial growth.
Frequent cartridge clogging: Cartridges can become clogged quickly, particularly in tanks that are overfed or overstocked. To avoid this, it’s essential to maintain proper feeding and stocking practices.
Risk to small fish and invertebrates: The intake can suck up small fish, shrimp, or fry. This can be easily prevented by covering the intake with a sponge. However, the sponge itself can become clogged quickly, even if it’s porous, so regular maintenance is necessary.

Sponge Filters

Sponge filters are a great, budget-friendly filtration option, especially for smaller tanks or delicate fish and fry. They operate using an air pump, which generates bubbles that move water up through the sponge. This movement creates water flow that draws water through the sponge, where beneficial microbes colonize the pores and help filter the water. For even better performance, some aquarists attach a powerhead to the top of the sponge filter instead of relying solely on the bubbles.

Regular cleaning is simple—just squeeze the sponge out in old tank water to prevent clogging and maintain optimal filtration.

Pros of Sponge Filters

Affordable: Sponge filters are one of the most inexpensive filtration options available.
Easy to use and maintain: They are simple to clean by just rinsing the sponge in old tank water.
Fry and shrimp friendly: The gentle flow of water makes them safe for small fish, shrimp, and fry.
Effective when properly sized: In tanks up to 50 gallons (~190 Liters), they can provide excellent filtration.
No parts to replace: Sponge filters have no cartridges that need frequent replacement.
Minimal leak potential: Since the design is simple and doesn’t involve a motor or complex components, the risk of leaks is very low.

Cons of Sponge Filters

Takes up space: The filter sits in the tank, which can make it visually unappealing and take up valuable real estate in smaller tanks.
Requires an air pump: You’ll need an air pump to power the filter, which could be an additional cost if you don’t already own one.
Difficult to gauge when to clean: Since sponge filters don’t have a visible indicator for when they’re clogged, it’s easy to forget when it’s time to clean them.
Limited for larger tanks: Sponge filters are generally not suitable for tanks much larger than 50 gallons, as they would be ineffective in such large volumes of water.

Canister Filter

Canister filters are highly effective filtration systems consisting of a large container that holds different types of filter media. Water is pumped through the canister, where it passes through the various media that handle specific filtration tasks, including mechanical, biological, and chemical filtration. The versatility of canister filters lies in the ability to customize the filter media to meet the specific needs of your aquarium. (More details on filter media will be covered in a separate section.)

While canister filters are incredibly powerful, they require diligent maintenance. Certain filter media can clog over time, and if debris accumulates in the canister, it can decompose and release nitrates back into the water. This is why canister filters have earned a reputation as "nitrate factories" in the hobby. Regular cleaning is essential to keep the filter running smoothly and prevent nitrate build-up that could affect water quality.

Pros of Canister Filters

Customizable filtration: The ability to select different types of filter media for mechanical, biological, and chemical filtration stages gives you greater control over tank maintenance.
Built-in UV sterilizer (in most larger models): Many canister filters come with a UV sterilizer, which helps to control algae and other microorganisms in the water.
Increased filtration capacity: The larger size of canister filters allows for more extensive filtration, making them suitable for larger aquariums or higher bioloads.
Storage-friendly design: Most tank stands feature a cabinet specifically designed to house canister filters, keeping them out of sight and organized.

Cons of Canister Filters

Maintenance challenges: Cleaning canister filters can be time-consuming and difficult, especially when dealing with clogs or buildup of debris.
Leak potential: While generally reliable, there is a medium risk of leaks, especially if the filter is not assembled or maintained properly.
Improper media selection: Using the wrong filter media can lead to issues with water quality and filtration, making it essential to choose the right materials for your system.

Sumps

Sump filters are typically used in larger aquariums due to their flexibility and ability to support various filtration methods. A sump is usually a separate tank, divided into multiple chambers to hold different types of filter media, live plants, and other elements that help further clean the water. The water from the main tank flows into the sump, where it is filtered through media or nurtured by plants, bacteria, or even algae. While sumps are highly effective, they are not typically sold as pre-made units, so hobbyists often build their own customized setups.

Sumps are especially valuable for those looking for a high degree of flexibility in filtration. Because they can hold a wide variety of filter media, live organisms, and even equipment like heaters, sumps are a great choice for advanced hobbyists.

Pros of Sump Filters

Highly customizable filtration: Sumps allow you to mix different types of filter media and filtration techniques. You can even incorporate live plants and algae to naturally clean the water.
Easy maintenance: Cleaning a sump is straightforward, as it’s often less cluttered than other filter types and offers plenty of room for access.
Large capacity: The size of a sump can be as large as needed, allowing you to use the biggest tank that fits under your main aquarium for maximum filtration efficiency.
Low clog potential: Due to their design, sumps have minimal risk of clogging, making them a more reliable option for larger tanks.
Conceals equipment: Sumps can house heaters, pumps, and other equipment out of sight, keeping your aquarium setup neat and visually appealing.

Cons of Sump Filters

Higher cost: Sumps are generally one of the more expensive filtration options, both in terms of initial setup and maintenance.
Leak potential: If not properly engineered, sumps can present a higher risk of leaks, especially if the chambers or seals are not well maintained.
Increased evaporation: Because water is constantly moving through the sump, this system can lead to greater evaporation rates, requiring more frequent top-offs.

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