This Phosphate Pad is a dense chemical filter pad which absorbs phosphate from your aquarium. In high concentrations, phosphate is a major food source for troublesome algae. Phosphate gradually accumulates due to overfeeding, lack of regular maintenance, and decaying organic matter. This media should be implemented as a preventative measure or treatment. The Phosphate Pad is not a substitute for regularly scheduled aquarium maintenance. Use a phosphate test kit to monitor your water quality regularly. These Pads can be cut and shaped to fit any filtration system, such as: Canister Filters, Hang-On Filters, Trickle Filters, Pond Filters, Wet/Dry Filters, Filter Cartridge Frames, and any other aquarium or pond filtration assembly. Great for both freshwater and marine applications. The pad measures 18" x 10".