Best hydro book?

Does anyone have a great book that they would recommend ?

For general hydro knowledge the book How-to Hydroponics is very good. Talks about all of the systems and instructions on how to make them

For cannabis specific and less hydro, no one beats Cervantes and his medical mj growers bible.

Cervantes' Medical Grow Bible has a lot of great information, but the hydro section is not very extensive. However, most of the information is universal as far as nutrients, deficiency symptoms, and things you'd generally want from a book on growing cannabis anyways.