Marina Betta Gravel - Tri-color Blue - 500 g Add a splash of color to your betta aquarium with Marina Betta Decorative Gravel. The expoxy-coated gravel has smooth rounded edges to protect delicate Betta fins. The gravel is inert, preventing it from having any adverse effects on water chemistry. For freshwater aquariums. Tri-Color Blue Gravel. Key Features : Decorative feature for Betta aquariums Smooth, rounded edges to protect delicate fins Pre-rinsed & Dust-free Epoxy-coated, will not adversely affect water chemistry Stone type: Tri-Color Blue Size: 4-5 mm