How do I know if it's safe to add rocks I find to my tank?
First you need to make sure anything alive on them is dead. This is accomplished by boiling the rock for awhile. This is similar to how you would sterilize a baby bottle. Once this is done drain and dry the water and then put the rock in vinegar or some type of acid. If the rock begins to bubble like crazy it will likely break down in your tank and/or affect the pH and hardness of your water too much.