Test it for carbonates, which could mess with your water hardness and pH. You can do this with vinegar. Put some vinegar on it, and if you see fizzing, it has (usually pretty high) carbonate content.
One way to be very sure is to use some Hydrochloric Acid on it. If you have an API test kit for ammonia - I believe one of the bottles is HCl - it should be the one with a "corrosive" warning label, but I can make sure when I get home.
I don't think you have to worry about Feller Stone rainbow rock much though. It's just a sandstone with some quartz, k-spar, and plag - which shouldn't do anything to your aquarium.
Just do a quick vinegar test, and then soak it in some hot water for a couple hours, and I think you're good to go. |