Penn Plax Pro-Carb Activated Carbon Crystals for Aquarium Remove toxins, harmful chemicals, and odors from your aquariums water with our specially formulated Pro-Carb filter media. Pro-Carb contains laboratory quality, fast acting activated carbon crystals to remove harmful chemicals, odors, discolorations, and other contaminants from aquarium water. Maximizes filter efficiency by helping to remove harmful toxins and ammonia from the aquarium water. Penn Plax Pro Carb formula will keep your water clear for 4 to 6 weeks. Pro Carb leaves your water looking crystal clear and is safe for use in both fresh and saltwater fish tanks.