Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Run some tap water into a glass and test it right out of the tap, then set the glass aside and test it 24 hours later, then 48 hours later.
Do a second glass or bowl at the same time and put in one of the questionable rocks. Same testing procedure: 24 hours, 48 hours, then several days later.
Test for pH, GH and KH. TDS, if you have a meter.