Tufa Rock Garden Pictures

gallon aquarium for his birthday and we're decorating it now. We want it to be as natural as possible. We'd been looking for stones, slate actually, so we could make ledges and levels for fish to hide and be happy as possible. We intend on using as many fish as possible in this tank size...we'd like them to be schooling and we'd like them to be neon tetras.

Now, back to the original question. What has to be done to the tufa to make it ready for a tank? Won't it leach out too much base making the water very hard?