i've purchased both fresh and salt water books from bookstores before but from my experience with them, the info was slightly dated (ie. watts per gal), and usually 5% of the book is an outline on how to set up and maintain an aquarium and the other 95 was general info on different species of fish/plants/corals. The majority of the indepth articles i usually found online. The book themselves to me makes more of an coffee table books. But maybe i just happened to choose the wrong books. im curious to see what's suggested =) maybe i'll get a few myself. I did hear tho that a lot of people have liked the diana walstad book.
I've learned most of what I know from the internet (back in the usenet days, before the internet had pictures ).
For the most part, I've found a large majority of aquarium books tend to be overly basic, or really specific to a certain species.
There are quite a few exceptions I've ran into over the years, but unfortunately I can't remember any of the titles off the top of my head.
I've recently read (and purchased) Walstad's book, and thought it was really great. It probably helps to have a bit of a science background, or at least be scientifically literate, but I think she does a fairly good job of explaining things.
I just got Walstad's book in the mail last week and so far my first impression is like... why so much science! I think I can probably jump ahead to find some sections that are more relevant to things I might want to read but right after jumping in, it seems excessively in depth about things that I'm not really interested in. (ie: toxic levels for various heavy metals) I'm glad to hear you liked it though, I probably need to spend more time getting deeper into the book.
There is plenty to learn from Walstad's book, although I agree it gets a bit thick in places. Still, better too much than too little, eh? Clearly THE original on low tech aquarium keeping.
I found "Aquarium Plants" by Cristal Kasselman to be very useful. For example, she really digs in to the different amazon sword varieties and helped me choose what was just right for my situation. I understand she has a newer version (the english translation you find is from ~1999) that has not been translated into English yet.
For general info, reading articles and specific threads on the net are as good as it gets, but look to published books like the two above for depth.
My first one was "Encyclopedia of Aquarium Plants" by Peter Hiscock. It is a very good book for a beginner and has a lot of stuff about setting up and maintaining aquariums, aquarium lights, algae and plants.
I learned from this book about a "siesta period" that helps to control algae.
"Ecology of the Planted Aquarium" is also a good book but as lochaber stated above a science background would be a plus.
I'm currently reading The Optimum Aquarium by Kaspar Horst and Horst Kipper. It's the Dupla book somewhat favoring their products (like ADA), but it's amazing how much they knew back then. I'm not finished with it yet, but it's a good read.