Dear ghstrider,
Good Morning! Aquarium size is a concern. Planktivorous fish are accustomed to having free range of the open water. Placing Angels into tight quarters can promote stress and bring any number of pathogens upon them. A single individual will do well in a traditional four-foot long aquarium, provided it has been aquascaped. This means the fish should have adequate hiding spots, which enable it to find areas of quiet and darkness, yet afford the fish plenty of open water at the front of the aquarium. Placing two or more individuals into the same aquarium is possible in four-foot long aquariums provided other fish are kept to a minimum. A preferable tank size is six-foot long for a pair these natural swimmers.
Ginger K.
LiveAquaria
Drs. Foster and Smith