Do you mean natural gravle, for landscaping? If so, thats what I use. You just need to make sure that you rinse it with hot water 7-12 times. It has a chance of altering your water's chemistry. But that has never happened to me. Good Luck,
Ron
Any substrate is suitable as long as it doesn't dissolve in water and has no sharp edges to it. In an aquarium, pea gravel is usually suitable and is a lot cheaper to buy from a builders merchant than an lfs. However it wil need a lot of rinsing before use.
