I have some new rocks, well stones really I guess. They're really neat and smooth and rounded so I thought they would look really nice in one of my aquariums. How do I tell if they're aquarium safe though? I don't want to throw off the PH.

Also, how do I clean them? They have moss and dirt all over them.

Try pouring vinegar on them, if they fizz then they're not safe. If they don't fizz they're fine.

As for cleaning I would first give them a good scrub with a toothbrush and maybe vinegar. That ought to get rid of most of the dirt. Then rinse well.

Soaking in a bucket of water will 'soften up' any particularly muddy portions of the rocks, making them easier to scrub.