post dimensions. If dimensions are 2 feet wide, than a clown knife with no tank mates is possible. Another option is a shoal of about 5-6 African brown knife fish with other small tankmates.
A clown knife might be ok. The length is kinda short. A shoal of 5-6 ABK with some of the smaller bichir species (senegal, mokelembe, delhezi, palmas palmas, palmas polli, palmas buettikoferi, retropinnis) would be your best option.