Can anyone give me some tips on how to tell if a rock is safe for my tank?
I found some really cools rocks on a beach in Mexico. I'm pretty sure they are slate (flat, smooth, and black), and I think they'll look great with the black substrate in my community tank.
Is there a way I can determine that they're safe for the tank? I read somewhere that you can test rocks by putting a weak acid on them (such as vinegar), and if the acid doesn't bubble, it's safe.