Complete Guide to Troubleshooting Hang-On Aquarium Filters

Hang-on back aquarium filters are popular with both beginner and experienced aquarists. Their easy installation, compact design, and combination of mechanical, biological, and chemical filtration make them ideal for maintaining a healthy freshwater setup.

The All Pond Solutions HOB filter range covers a wide variety of tank sizes, helping keep your aquarium clean and your fish happy. Each model operates slightly differently, so always keep your instruction manual handy for setup and maintenance. If you need a copy, it can be found on the relevant product page under the “Product Instruction” tab.

Why Regular Filter Maintenance Matters

Over time, filter sponges and biological media collect debris, and activated carbon (if included) loses effectiveness. Without regular maintenance, water flow can slow and harmful ammonia and nitrite levels may rise, putting fish at risk.

Routine filter maintenance helps to:

• Maintain healthy, stable water quality

• Prevent bacterial imbalances

• Extend the lifespan of your filter

• Reduce noise and performance issues

All Pond Solutions offers a full range of replacement spares for perishable components, making it easy to keep your filter running efficiently for years.

Replacement Parts for All Pond Solutions Filters

Having spare parts on hand simplifies maintenance and helps keep your aquarium water clear and healthy. Common replacement spares include:

HOB-500:

• Replacement filter foams

• Replacement impeller & shaft

400-HO, 500-HO & 600-HO:

• Replacement impeller

• Replacement O-ring pack

• Carbon cartridges

500-HO+ & 800-HO+:

• Replacement impeller

• Replacement O-ring pack

• Replacement filter foams

• Media cartridges

Common Issues and Troubleshooting

Even reliable filters can occasionally experience issues such as reduced flow, noise, priming difficulties, or air-like sounds. The steps below will help you diagnose and resolve the most common problems safely and effectively.

Safety First

Always disconnect your aquarium filter from the mains electricity before inspecting or handling it. Refer to your product instruction manual for model-specific guidance, especially the troubleshooting section.

Filter Won’t Turn On or Pump Water

• Check the power supply and socket (try a different socket if needed).

• Inspect the intake tube, motor housing, and impeller for blockages or debris.

• Ensure the impeller shaft is correctly aligned, undamaged, and fitted with rubber grommets at each end.

• Confirm the impeller magnet and plastic propeller are securely attached and not split.

• Rinse clogged filter media in established aquarium water only.

• Replace worn or damaged impeller parts if required.

• For UV models, ensure the UV bulb is correctly seated and functioning.

Gurgling or Loud Noises

• Trapped air (particularly common with the HOB-500) can cause gurgling. Priming the filter usually resolves this.

• Fill the filter housing with aquarium water before switching it on.

• Ensure the aquarium water level is high enough to maintain a proper siphon.

• Clicking or buzzing sounds often indicate a worn or loose impeller—clean or replace as necessary.

Low Flow Rate

• Rinse filter sponges and carbon cartridges in established aquarium water only.

• Check the intake tube and internal channels for debris buildup.

• Inspect hoses and pipework for kinks or blockages.

• Heavily stocked tanks may require more frequent media maintenance.

Filter Won’t Prime

• Most priming issues are resolved by manually filling the filter chamber with aquarium water before switching on.

• Topping up the aquarium water level can help establish a stable siphon.

• Persistent priming problems may indicate air leaks or worn seals that require replacement.

Air-Like Sounds – Is This Normal?

Yes. Air-like sounds are common during initial startup and priming and should stop once water begins flowing smoothly. If the sound continues:

• Refill the filter with water

• Recheck the aquarium water level

• Inspect the impeller and seals for wear

UV Not Effective (For + Models)

• Ensure the UV chamber is clean and dry.

• Replace UV bulbs annually for optimal algae and water clarity control.

• Regularly inspect seals and O-rings to maintain water-tight performance.

Final Tips

• Inspect your filter regularly to ensure all components are functioning correctly.

• Follow the maintenance schedule outlined in your instruction manual.

• For + models, routinely check UV bulbs and seals.

• Never clean filter media in tap water, always use established aquarium water to protect beneficial bacteria.

If problems persist after troubleshooting, the All Pond Solutions support team is always happy to help.