CaribSea Coraline Aquarium GravelDont settle for an ordinary gravel. Natural dramatic colors and textures combined with pH support characterize our CaribSea Coraline Aquarium Gravel products. These are coarser materials suitable for most undergravel filtration and fish systems or as an accent for finer sands anywhere where elevated pH values are desirable. Consider the Coraline products in brackish or Cichlid aquariums (Central American or African). Our substrates are purposely engineered and free of impurities such as ash, metals, pesticides, and silica which allows you to create a safe and beautiful environment for your fish and invertebrates. Precision grading makes system design a breeze!