I picked up some seashells for my Neos but they stink. I've boiled them for 15 minutes and rinsed but they still stink. Do i just try boiling them again? Is the stink bad for the fish or evidence of biological matter? There doesn't seem to be anything inside them. The shells are sea snail type but look like they've been dead for a while if there ever was anything inside them. Some are so broken there's so space for anything to get stuck inside.