Review on 🐠 Penn-Plax Filt-a-Carb Replacement Activated Carbon Cartridges (2 Pack) - Enhancing Chemical Filtration in Freshwater and Saltwater Aquariums by Kimberly Peterson

These cartridges are the perfect size for our gravel pack. These cartridges are not breathable. Our filter system is cleaned regularly and works perfectly without cartridges. We have had other cartridges without this problem. They're just kind of cushioned so the air doesn't come out. We opened 2 of the 3 packages purchased to see if the first was fake but the second was exactly the same. We tried spraying them with water from the sink. We tried soaking them in water but nothing helped. I'm returning for a refund.