Tank width is more important than length, IMO. The 300-gallon Deep Dimension, for example, would be a far better choice than a standard 300-gallon tank, which I believe are only 24" (or less) deep. Our tank is 36" deep, so he has plenty of room to turn around. 25" is not a small puffer (his body is larger than a regulation NFL football...) by any means but there is plenty of room for him and the other fish in our tank. He appears to have either stopped or dramatically slowed his growth in the last two years, so I suspect he is pretty much as big as he will get. A 72"x36" tank should be fine for one of these guys for life, but it is the bare minimum I would recommend.