Exo Terra Turtle Pebbles are river pebbles that have rounded over time in fast-moving waters. Their smooth texture prevents injury to foraging or bottom-dwelling turtles, and the color variations and patterns create a natural looking environment. Turtle Pebbles can be easily cleaned and reused by soaking in a large bucket of warm for 15 minutes, rinsing until all of the visible particles are removed. This size (8 - 10 mm) is safe for use with turtles with a shell diameter of 4 inches or less. To prevent accidental ingestion or the substrate, use the 10 - 20 mm size.