Gerbils like to take sand baths. The sand helps keep their coat soft and oil free. When selecting a sand make sure it is Chinchilla Sand as power and dust baths can get into their eyes and respiratory systems. The small aquarium bowl is great for keeping the sand contained. You can leave this in their tank and they will also use it as a bathroom which helps keep their cage fresh. If you leave it in their tank make sure you sift it daily.