Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Go to the local rock yards and see what there is. Bring home samples in a baggie. (A sharpie to label the bags is helpful). In the rock yard there will be broken bits and crumbs from the rocks.
Test the samples by setting up some jars of water (Whatever you will use in the tank- RO? Tap?), each with one sample of rock, and one with nothing (just the water).
Test GH, KH, pH and TDS (or as many of these tests as you have) every few days.
Whichever rock shows it is safe, that is the one you go get more of.