Altifrons can reach up to 12" in length supposedly, 10" is more common. They do much better living in a group. The Tapajos can reach 8", 6"+ average. Both are quite large to keep in a group in a 55 gallon tank. If you tried to maintain a group of geophagus in a 55 gallon as adults, not to mention the severum(s), you would find your nitrates very hard to keep low without excessive (every day water changing) maintenance. These fish are also sensitive to HLLE (Hole in the head disease) if kept in crowded, poor conditions.
If you wanted eartheaters, the Ram cichlids in the mikrogeophagus genus would be more suited to a 55 gallon. They are "dwarf geophagus", don't do as much earth sifting, but are in the family. Can also be kept in small groups.
