Hi..I have a well established healthy tank for the past 6 months. I just recently came back from a trip to the Dominican Republic. I collected some very pretty rocks,,maybe coral. White and pink/ smooth. I also got a few small shells. Are these safe for my freshwater aquarium? I thought I would boil them first to remove any germs..but, I don't want to add them if there could be a problem. Any thoughts?? Thanks so much, Elaine