I use 15qt for juveniles, shoe box for hatchlings... 32 qts are great for adult males and younger/smaller girls. 41-42qt seem to do well for most adult gals- although I'm looking to ad a CB 70 rack or 2 which would be perfect for any BIG gals, since I've a few BP girls that are over 5 ft 6+ lbs... I've got my a few of the biggest in Iris 900s but it's over-kill.