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.

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The above post is fictional and should in no way be taken as truth.

If I were to grow cannabis, I would only do so to supply myself and my close friends. Doing this would take myself and my friends out of harms way by knowing the source of our cannabis, as well as take hundreds of thousands of dollars off the black market annually. It would also lower the demand of black market cannabis, and would ultimately help keep cannabis out of the hands of minors.