The Fluval FX4 Magnetic Impeller Assembly is the genuine replacement magnetic impeller assembly for the FX4 High Performance Filter — the single part most likely to fix a filter that has gone quiet on flow or loud on noise.

Key Features

• Made for the FX4 High Performance Filter
• The impeller is the wear part in any canister filter. It is the first thing to replace and the cheapest
• A worn impeller shows up as reduced flow, a buzzing or grinding noise, or a filter that will not restart after a power cut
• Genuine part — the magnet strength and the blade profile both matter, and generic impellers run noisily
• Made by Fluval, the aquatics brand of Rolf C. Hagen, which has been building aquarium filters since 1975

Fitting It

• Unplug anything electrical before putting your hands in the tank
• Disconnect the hoses and take the unit to a sink rather than working over the tank
• Check the old part against the new one before fitting. If they differ, stop and check the model number
• A smear of silicone lubricant on an O-ring before reassembly makes the next service much easier and helps the seal sit properly
• Prime the filter and watch the first few minutes of running for leaks before you walk away

Good To Know

• Replace the impeller before assuming the motor has failed. It fixes the great majority of canister problems
• Clean the impeller well and the shaft it runs on. A new impeller on a scored shaft will not last
• Keeping a spare in the cupboard means a failure on a Friday night is an inconvenience rather than a crisis
• A genuine Fluval spare part. Check the model number against your unit before ordering — Fluval part numbers look alike and do not cross over between series
• Fluval sells these individually so a filter can be repaired rather than replaced, which is usually the cheaper and greener option
• Keeping a spare impeller and O-ring in the cupboard saves a tank when something fails on a weekend