i agree with nick goody, a 2.5 is pretty small, i keep two of my bettas in their own 2.5s, but i really wish that i had gotten 5s instead.
2.5s really aren't worth the money, for everything that i bought for mine (10 for the tank 16 for the heater 16 for the filter, decorations, gravel etc) and NOT including a hood, i could have just gotten two more of my favorite 5 gallon kits.
http://www.petsmart.com/product/inde...ductId=2752239
(it says $45 on the site, but if you just sign up for a pet perks card which is completely free in the store it's only $36)