I use crushed coral and silica in my planted tank..its great..I think the
dissolving helps add trace elements for the plants...
Using some aragonite can be helpful if you have very soft water, or want to
keep Rift Lake cichlids. But most people find using 100% coral sand or
aragonite in a freshwater tank does crazy things to the pH. Especially in a
small tank. I really don't recommend it for beginners.