Great links above, however if you are feeling particularly challenged and are looking for good marine chemistry texts, I'd suggest books by Stephen Spotte. It's certainly not light reading, but it's great info. You can preview one of his books on Amazon.
I like:
Captive Seawater Fishes: Science and Technology
and
Fish and Invertebrate Culture: Water Management in Closed Systems
or a earlier work
Seawater Aquariums: The Captive Environment
Martin Moe also has several nice books that are very readable. You don't need a chemistry degree to follow them and they are well written.
Marine Aquarium Handbook: Beginner to Breeder
or
The Marine Aquarium Reference: Systems and Invertebrates
Martin Moe had many early marine husbandry successes, his tale of raising Orchid Dottybacks over 14 years ago is still quite good today for those interested in breeding fish:
Breeding the Orchid Dottyback, Pseudochromis Fridmani: An Aquarist's Journal
-Rob