I have a 50G Brackish tank with 3 GSP, 3 Glass fish, 1 Needle fish, 1 Dragon Goby and 2 Black Tip Sharks. I had 2 puffers but I saw a gsp in the pet store that looked kinda sick. Almost black other than the green adolescent spot on the forehead. I was gonna buy him but thought against it. Figured he would die. 2 Weeks later I returned to the store to find him still there same colouring and still alive. I figured he's got a great will to survive to I bought him. He doesn't eat as much as the other 2 puffers I have. And his belly shrink shortly after he eats. While my other 2 look like porky the pig. He lightens up after feeding, but then goes dark about an hour later. He eats my plants as well. The other 2 gsp's won't touch the plants but he does. I've had him for about 9 days now and still behaves the same. I feed them frozen krill, bloodworm, brine, dried blood worm, flakes and snails every 3 days. But the little guy still goes black after an hour while the other 2 are always very light green. Any suggestions on his behavior or what I can do to get him to 100% again? Or is it a lost cause.