The JBJ 3-in-1 Filter Pad is an aquarium filtration media designed to provide simultaneous chemical and mechanical filtration. the pad combines three specific layers: a phosphate reducer, a nitrate reducer, and activated carbon. “Phosphate reducer, nitrate reducer and activated carbon Fits perfectly in over head compartment.” Key Features: Phosphate & Nitrate Reduction: Actively targets and removes excess nutrients in the water, helping to prevent unwanted algae outbreaks. Activated Carbon: Eliminates odors, discoloration, and organic pollutants from both freshwater and saltwater aquariums. Custom Fit: Typically measuring 16.2 × 28 cm, it can easily be cut to size to fit overhead filters, sumps, or baffle trays. JBJ Over Head Filter (OHF) 3 in 1 Filter Pad (MrAqua OHF Compatible): Freshwater and marine tank use Filter Pad size: 28cm (L) x 16.2cm (W) Filter pad consists of: 1x White Filter Wool 1x Phosphate Reducer Pad 1x Nitrate Reducer Pad 1x Activated Carbon Pad