Welcome to Reef Central!
Here is the recommended requirements of this wonderful little fish.
QUICK STATS
Minimum Tank Size: 30 gallons
Care Level: Moderate
Temperament: Peaceful
Reef Compatible: With Caution
Water Conditions: 72-78° F, dKH 8-12, pH 8.1-8.4, sg 1.020-1.025
Max. Size: 4"
Color Form: Black, Blue, Orange, Tan, Yellow
Diet: Omnivore
Compatibility: View Chart
Origin: Hawaii, Indonesia, Sumatra
Family: Tetraodontidae
This said IMO you will need a little bit larger tank to keep this guy. What happens when a fish is in a tank that's too small is it creates aggression on the part of that particular fish, even if they aren't aggressive to begin with.
With that said Petco is having their $ per gallon sale starting this weekend and usually runs for a month. YOu can get a 30 gal for $30 and not have any different requirements on your tank equipment.
A pair of clownfish along with this one will be fine in a 30 but maybe not so much in a 20. Going just that 10 gal difference opens up a lot of different choices for you over the 20.
Good luck in whatever you decide on and enjoy the site. Make sure you read the stickies at the top of each forum as they contain much information. There is always someone willing to offer advice so your animals are very happy!
Welcome!