Target sells several kits such as these for $10 - $20. Not a bad price for an afternoon of science fun! We put together the sodium something or other mixture (sorry, I don't remember what it was!!!) and dropped in the colored salt rock.
Within a few minutes coral was already growing!
In a few hours, the coral had reached its maximum height.
Very cool! This was an easy experiment to set up and my daughters had fun checking it every few minutes to see changes. As I said at the beginning of this post, a cheap science kit for several hours of afternoon science fun!