Modular Aquarium Filters also called Inline Aquarium Filters, are specialized filter types that perform specific tasks. These specialized filter types can be linked together to create customized filtration systems, or used to enhance an existing filtration system. These 'modules' are available in biological, mechanical, chemical, heater and sterilizers forms to name a few.

Typically the modules are linked together, beneath the aquarium, and operate with either a submerged or external pump on a closed loop setup that forces the aquarium water through the linked modules.