The Carib Sea Coraline Aquarium Gravel is a high-quality, durable gravel that is perfect for use in aquariums. The gravel is made of coraline, which is a form of calcium carbonate that is both beautiful and useful. The gravel is also precise, so it allows for free flow of nutrients and oxygen to the nitrifying bacteria. It also resists packing channeling and anaerobic “dead spots” beneath the rocks and coral. The Carib Sea Coraline Aquarium Gravel is also pH-balanced and has a low iron content, so it won’t affect the PH or color of your water.