I have these old rocks I got from the beaches in Italy when I was a kid that I'd like to put in my FW tank. These rocks have been sitting for over 20 years. My dad used to have them in his FW tank but he remembers his fish dying so he took them out. They have been sitting in his empty tank all this time. I liked to put these rocks in as a top layer over some other gravel. Anyone see any problems with this? Whats the best cleaning method to use for these? I should say that I'm just starting off my tank beginning the cycling process with no fish yet. Thanks for the help.