Replacement Laguna PowerFlo Underwater Filter Foam PT550 by Zanyzap, 2 Pack Fits Laguna PowerFlo Mechanical Underwater Filters (PT-500) Fits Laguna PowerFlo Max Biological Underwater Filters (PT-505) Each package contains two filters. Open the package and seperate the two filters before use. Provides biological and mechanical filtration to your pond filter Bulk packaged to save you money and protect our environment