Hello roc, I have been a fish keeper for many years now and I do have a green spotted puffer/leopard puffer. I have just joined this site recently because I love axolotls and they are hard to come by. I belong to three different fish forums if you would like their sites, I would gladly give them to you as, they have been very helpful to me.
When I first received my puffer about, two years ago, I had kept him in a 10 gallon freshwater tank. But, as the fish grows larger he/she will need more room and the salinity of the water will need to increase. Pay attention to the color of your puffers belly if, it's black usually it means there's something wrong but, my puffer will just turn black if he's not receiving enough attention. What do you feed your puffer? The beak on the puffer will keep growing like gerbils teeth. It must either be fed something to file it down(snails, clams, etc) or you must manually trim it yourself. This fish is a lot more work than most people think. I have a 10 gallon tank that I specially breed snails just for the puffer and I upgraded to a 72 gallon saltwater tank. As the puffer grows it will need a full saltwater tank or your puffer may not live long. All the information I have provided has been from my own personal experience and much research. Here are some very informative websites I would definately recommend taking a look at: (
http://www.aquatic-hobbyist.com/profiles/brackish/gsp.html) <~~~~Look at the water chemistry on that first site. (
http://greenspottedpuffer.net/) <~~~This one is probably the most helpful when it comes to the GSP.
I would also like to add that the GSP will get more aggressive as he/she ages. It may or may not be fin nipping right now but mine is about it's max size now and eats large rosies, mollies, jumbo size cocktail shrimp, full size crayfish, freeze dried krill, crabs, snails, meal worms(not recommended, very messy) and anything else he can get into his mouth. The only reason he hasn't attacked my eel may be that the eel is too fast and three times the size of the puffer. He also tries to take bites out of my fingers while I'm performing any maintanence to the tank.
I know it is hard to remain cool when strangers are telling you that you're doing everything wrong, I have had experience with that myself. Sometimes it deters me from posting questions at all but, just take it with a grain of salt and do as much research as you can to better the life of your pets. Most people are just trying to help. Take care.