i agree - a common would need much more space.

as for visualy challenged fish - i guess it depends on how much time you intend to spend feeding them. i myself have a moor in with my other non-visually chalenged fish, and he gets along fine, but it does meen that i have to spend longer making sure that he gets his fair share of the food etc.

personally i would not suggest going for a pearlscale as i believe that they should have about 15 gals per one, but that is just my personal opinion.

i would reccomend something like a ryukin or a rachu, as they would be able to compete fairly with your oranda.

good luck.