I know how you feel right now but please don't get another one.
Did you pick up this fish in person?
If so, I'm guessing that you must've picked out the most active/desirable one..
Give it some time to get used to the surroundings.
These puffers are much more complex than people give them credit for - and they need to settle in when they first arrive. It may take a while, but you will notice a huge difference in their behaviour when they do.
I noticed that mine was much more active with no lights.
Have you got some floating plants?
You can also use paper towels under your lights to dim it down.
You may, to your discretion, try a tankmate while it's still young.
Choose carefully if you do. It may be on a trial and error basis.
I highly agree with the person who said to treat for internal parasites just in case.. I almost lost mine to an illness, and it's better to be preventative than panicking later... trust me on this.
Wait until they see you as the bringer of food, they'll be begging/dancing every time you walk up to the tank.
These are highly rewarding fish to take care of.
I really miss mine actually.. Probably the most fun fish I've ever had.
