Choosing an aquarium filter: beyond litres per hour

A filter is equipment you may use for years. The largest number on the box is not the whole story. Shortlist suitable models and ask how each would be maintained in your setup. An accessible filter is easier to live with than a powerful one that barely fits inside the cabinet.

What does the media do?

Mechanical filtration traps suspended particles. Biological media provides surfaces for beneficial bacteria. Some media combines both functions; EHEIM explains this for its mechanical-biological media. Check the arrangement recommended in the manual. A basket of ceramic media does not necessarily belong in the same position in every filter.

Compare three practical options

• Internal filter: check how much tank space it occupies, how you access the sponge and whether the outlet is adjustable.
• External filter: measure the cabinet, clearance above the filter and hose route. Ask which valves, hoses and media are included.
• Sponge filter: check whether you also need an air pump and which connections, backflow protection and air supply the manufacturer specifies.

For each candidate, record dimensions, power consumption, replacement-part costs and maintenance steps. Ask about suitable intake protection if you plan to keep small animals. This compares complete solutions rather than isolated pumps.

A checklist to take shopping

Bring the net water volume, planned inhabitants and a cabinet photograph. Ask what flow the model can provide in your setup, accounting for media, hoses and height differences. Have the retailer explain how to position the outlet and recognise when maintenance is due. Do not apply one universal turnover figure without checking the application.

Care without replacing everything

Keep the manual with your journal and follow its shutdown and restart procedure. Biological media does not need to be sterile: gently clean it in removed aquarium water when needed and avoid replacing all biological media together. The RSPCA provides further guidance on filtration and water quality.

Record what you do at each maintenance session. Check connections, leaks and flow after restarting. When changing the setup, make one clear adjustment and write it down. That makes comparisons and troubleshooting much easier.