I find that 2 species are sold as green spotted puffers, the more common being the Tetraodon nigroviridis that averages 6" as an adult, and the T. fluviatus which is darker and an inch bigger. Both say that they need brackish water as adults and unlike many brackish species you should use Marine salt, not aquarium salt.
I have not kept puffers except for a couple dwarfs I had for a couple days and stupidly put into a tank full of angelfish.
Several sites say that they should be kept at a SG ranging from 1.015-1.022 with most leaning towards the upper end of the range. They are not usually considered reef safe as they love to eat inverts. They have strong beaks and can crush snails and hermits as well as pick apart corals and tube worms.
Here is a link to a site I found informative.
http://www.wetwebmedia.com/BrackishSubWebIndex/gspsart.htm
This picture is the T. nigroviridis