The diatoms could definitely be connected to lighting problems. While the diatoms will go away on their own, a few more types of snails might help (certith and nassarius are good).
This is a nice site for basic info on various corals:
www.asira.org - Coral CareĀ*
I'd highly recommend getting the book
Aquarium Corals by Eric Bourneman. It's about $30, but it's got great info on all types of corals, coral biology, coral diseases, needs of most corals available in the trade, etc.