This is a discussion on feldspar within the Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; -->
is Feldspar a safe rock for use in fishtanks?...
I've used it before, however i cleaned it throughly and ran the tank with it and checked the levels frequently before I added fish.
So setup a small tank if you can and run it in there after you wash it good, use some vinegar etc to clean it wash it really good with water... then test it if you can.
Some feldspar does contain calcium, so I would test it first to see if it will raise your hardness and pH. You could leave it in a bucket of water for a while, periodically testing pH and hardness, to see if it'll affect your aquarium water.
