'Gator pipes are actually one of the LARGER SW pipes, and they'd do better in a larger setup than a 20 gal (I'd go at least 29 gals for a pair), however, the space in a 40 gal would be better. They tend to take to frozen more easily than many pipes, partially due to their size, and are actually classified by many as a "pipehorse" because they have prehensile tails like a SH.