i think i read that your tank is a 180 so a lima shovelnose will probably work. an 6" F/S or bigger will go with your F/S you have now. im guessing that all polys will work cuz ive seen just about all the species in with gars. and as far as knife fish i would say clown knife, african knife but not permanantly cuz i think they max out at only 8 or 9", or a good size black ghost knife.