Without altering the consistency or pH levels of the water they sit in, the Pisces Natural New Zealand Gunsmoke Gravel provides a habitat evocative of your fish's natural habitat, rendering an environment for them to interact with and use as an area of natural disposal. Gravel is known to host “good bacteria” that is essential to eliminate waste and debris build up, extending the life of your fish and your aquarium. Being only 3-55mm in diameter, these granules of gravel are the perfect size for a safe and fun aquatic environment.