The Fluval AquaClear 20/30/50 Intake Strainer Sponge is a pre-filter sponge that slips over the intake stem of AquaClear power filters (models 20, 30, 50). It effectively blocks large debris, small fish, or shrimp from getting drawn into the filter, while also providing extra mechanical filtration. This sponge helps protect delicate creatures like fry or shrimp and keeps the filter media from clogging as quickly, contributing to clearer water and easier filter maintenance.