Hello,
I already did this in my tank. We have been mining for years. My 55 gallon has been set up for several months now and it has done fine. The current of the water will act like a very slow tumbler on many of your stones and some become very beautiful. Do boil them gently first and rinse well. I would not suggest any really soft or extremly pourous stones. I have ruby,garnet,amyethyst,opal,pearl,quartz,topaz,peridot,e
merald,sapphire, etc large and small, cut and natural, and have had no problems. I have platys, tetras, molly's, guppies and there seems to be no issues so far. In the first few weeks you may need to vaccum once a week depending on how large of stones you put in until they settle in the current and the softer outside covering of some of the natural gems loosens a tiny bit. I did this as an experiment because no one really knew and so far has turned out beautiful and I have even had fry...have fun and let me know how it goes!