A filter cartridge does not announce when it stops working; the ammonia and odour it was trapping simply start building up again, which is why a fixed replacement schedule matters more than watching for cloudy water.

This is a replacement power cartridge for the Marina i25 internal filter, model code A134. Water is drawn through the centre of the cartridge first into a zeolite chamber that removes ammonia, then into an activated carbon chamber that takes out pollutants and odours, before passing through a floss layer that traps dirt and debris. Marina recommend replacing it every 4 weeks.

• Replacement cartridge for the Marina i25 internal filter (model A134)
• Two-chamber design: zeolite then activated carbon
• Floss layer traps dirt and debris
• Marina recommend replacing every 4 weeks
• Pack contains 2 cartridges

On fit. This is specific to the Marina i25 internal filter and not a universal cartridge — check the model on your own filter before ordering, since a cartridge built for the wrong housing will not seat properly. No dimensions are given beyond that it is designed to fit inside the i25's own chamber.

Who it's for: Marina i25 filter owners working through their routine maintenance schedule, buying two cartridges at once rather than one at a time.