Hang-On-Back (HOB) Filter

The Hang-On-Back filter is a popular, compact filtration solution that clips directly onto the rear rim of your aquarium. It draws water up through an intake tube, passes it through a filter cartridge or custom media, and returns it via a waterfall-style spillway. HOBs are a favourite for nano tanks and setups where simplicity and ease of maintenance are priorities.

How It Works

An internal impeller draws water up from the tank through a submerged intake tube. The water flows through a media chamber — typically containing a sponge, activated carbon, and sometimes a biowheel or ceramic rings — and is returned to the tank over a weir, creating gentle surface agitation.

Filtration Capacity

• Mechanical: Built-in sponge or filter pad catches debris.
• Biological: Some models include bio-wheels or space for ceramic media.
• Chemical: Replaceable carbon cartridges remove odours and discolouration.

Best Use Cases

• Nano Tanks (10–40L): Perfect for small shrimp or betta tanks.
• Quarantine / Hospital Tanks: Easy to set up and remove quickly.
• Beginner Setups: Low cost and minimal learning curve.
• Supplementary Filtration: Used alongside a canister for extra surface agitation.

Customisation Tips

Many aquascapers replace the factory cartridge with custom media for better performance:

1. Remove the disposable cartridge.
2. Cut a sponge block to fit the media chamber.
3. Add a mesh bag of ceramic bio-rings or Seachem Matrix on top.
4. Optionally add Purigen for water polishing.

This approach avoids the cost of replacing cartridges and provides significantly better biological filtration.

Trusted Brands

• AquaClear: Industry standard with a large, customisable media basket.
• Seachem Tidal: Excellent flow control and self-priming.
• Fluval C Series: Multi-stage filtration in a compact form.
• Oase BioStyle: Slim profile, modern design.

Pros & Cons

Advantages

• Affordable: Low upfront cost.
• Easy Maintenance: Open the lid, swap media, done.
• Surface Agitation: Waterfall return oxygenates the water.
• Compact: No cabinet space required.

Considerations

• Visibility: Hangs on the back of the tank, visible from behind.
• Limited Capacity: Less media volume than a canister.
• Noise: Waterfall can be audible, especially as water level drops.
• Evaporation: Open design increases evaporation slightly.
• Not for Large Tanks: Insufficient for tanks above 100L as the sole filter.