Common Internal Aquarium Filter Problems (And How to Fix Them)

Internal aquarium filters are a space-saving and effective filtration solution for small to medium fish tanks. Popular models such as the AllPondSolutions 500L/H Aquarium Internal Filter, 800IF, and 1200IF are widely used thanks to features like venturi aeration, replaceable filter sponges, and adjustable flow rates.

However, even the most reliable internal aquarium filters can develop problems if they are not cleaned and maintained correctly. Understanding common internal aquarium filter issues and how to fix them is essential for maintaining clean water, healthy fish, and stable biological filtration.

We provide spare parts for all our internal aquarium filters; just be sure you know which model you own and purchase only from the dedicated spare parts section of our website, selecting components that are fully compatible with your unit.

An internal aquarium filter plays a vital role in keeping tank water clean, oxygenated, and safe for fish and plants. When an internal filter becomes noisy, stops working, or underperforms, water quality can deteriorate quickly. Fortunately, most internal aquarium filter problems can be resolved with simple checks and routine maintenance.

Safety First: Before Maintaining Your Internal Aquarium Filter

Before carrying out any inspection or maintenance, always disconnect your aquarium filter from the mains electricity supply. Refer to your product instruction manual for model-specific troubleshooting advice, especially when handling electrical components.

1. Reduced Water Flow or Blockages in Internal Filters

Problem: Weak or reduced water flow from the filter
Cause: Filter sponges and foam pads trap debris over time, restricting water movement

How to Fix Reduced Flow:

• Rinse filter sponges in old aquarium water only to preserve beneficial bacteria

• Clean the intake tube, impeller, and internal housing regularly

• Check venturi nozzles for debris or algae blockages

• Monitor flow rate — a noticeable drop usually indicates clogged media

• Clean the impeller monthly to prevent waste buildup

Maintaining good water flow is essential for effective mechanical and biological filtration.

2. Internal Aquarium Filter Making Noise or Rattling

Problem: Excessive noise, rattling, or vibration
Cause: Debris in the impeller, worn parts, or missing rubber grommets

A low, consistent hum is normal for motorised internal filters. However, loud rattling or vibration usually indicates an impeller or shaft issue.

How to Fix Noisy Internal Filters:

• Remove the motor housing and clean the impeller thoroughly

• Inspect the shaft for algae, plant matter, or trapped waste

• Ensure the plastic propeller is securely attached to the magnetic body

• Check that rubber grommets are fitted correctly at each end of the shaft

• Replace worn or damaged impellers if necessary

• Placing a small piece of foam between the filter and aquarium glass can help absorb vibration

3. Internal Aquarium Filter Stops Working

Problem: Filter stops running or works intermittently
Cause: Power supply issues, blocked intake, damaged impeller, or low water level

How to Fix a Filter That Has Stopped Working:

• Check the power supply, plug socket, and fuse

• Always use a drip loop to prevent water reaching the plug

• Inspect and clean the impeller and shaft

• Replace worn parts such as impellers if required

• Ensure the filter is fully submerged, as internal filters cannot operate dry

A damaged impeller may spin freely through 360 degrees and should be replaced immediately.

4. Cloudy Aquarium Water Despite Filtration

Problem: Cloudy or murky aquarium water
Cause: Insufficient filtration capacity or poorly maintained filter media

How to Fix Cloudy Water:

• Upgrade to a higher-capacity internal filter such as the INFIL-1500 if needed

• Add additional biological or chemical filter media

• Avoid cleaning all filter media at once to protect beneficial bacteria

• Maintain consistent cleaning schedules to support water clarity

Venturi Not Producing Bubbles?

Problem: Venturi aeration system not working
Cause: Blocked airline, damaged tubing, or incorrect setup

How to Fix Venturi Issues:

• Inspect airline tubing for kinks or damage

• Ensure the airline is securely connected to the filter

• Keep the black venturi valve outside the water

• Fully open the valve to allow air intake, then adjust aeration as required

• Remember: you can only use the venturi or spray bar, not both at the same time

Maintaining Filter Media for Better Aquarium Performance

Proper maintenance of internal aquarium filter media is essential for long-term performance and water quality. Internal filters typically use three types of filtration:

Mechanical Filtration

• Provided by sponges or foam pads

• Traps solid waste and debris

• Rinse every few weeks in aquarium water

• Replace every 6–12 months

Biological Filtration

• Ceramic rings or bio-media house beneficial bacteria

• Converts toxic ammonia into safer nitrate

• Clean gently and replace only when breaking down (every 12–18 months)

• Never replace all biological media at once

Chemical Filtration

• Activated carbon or zeolite removes dissolved impurities

• Improves water clarity and odour

• Replace activated carbon every 2–3 months

Avoid cleaning filters during major water changes or when introducing new fish to maintain biological stability.

Replacement Media & Spare Parts for Internal Aquarium Filters

Keeping spare filter media and components on hand helps maintain uninterrupted filtration. Replacement foams, ceramic media, impellers, and accessories are widely available and should be replaced as part of routine maintenance to prevent blockages and performance loss.

Final Tips for Maintaining Internal Aquarium Filters

• Choose the correct filter size, aim for 5× tank volume per hour

• Clean internal filters regularly and follow recommended replacement schedules

• Switch the filter off briefly during feeding to prevent food entering the unit

• Check hoses, fittings, and impellers for air disturbances

• Keep spare parts such as impellers or UV bulbs available

• Using the correct internal aquarium filter with suitable spares helps maintain clearer water, healthier fish, and a more stable aquarium

If problems persist after troubleshooting, customer support is always happy to help.