Put some vinegar on the rocks if it fizzes don't use it if it don't it will be fine. As far as cleaning them rinse under hot water and scrub with a brush to get any dirt etc off. Don't use any chemicals to clean because some rocks can absorb the chemicals and release them in your tank later. Some people boil the rocks I don't suggest doing this however rocks can and have exploded when boiling, exploding rocks would not be a good thing.
Posted on mobile.monsterfishkeepers.com