For the shaping of aquaria and terraria. They are easy to clean and do not affect the water quality. Are very durable and look beautiful in every aquarium and terrarium. These Hobby Guilin Rocks are near-nature rocks which ensure a natural look inside the aquarium. As they are manufactured from a safe inert poly resin material they affect neither the chemistry nor the clearness of the water. Their low weight obviates possible damage to the habitat. Approximate Sizing: Small - 20 x 10 x 12 cm, Medium - 23 x 11 x 21 cm, Large - 27 x 16 x 28 cm.