black ghost knifefish mostly are shy, need place to hide, sensitive to water quality, and are best kept SINGLY in tank where they can get live, meaty foods without much competitions. If it does not eat during normal feeding time, you have to feed it when the light are out (and all other fishes are asleep), or use a PVC tube to pour frozen boodworms directly into its hiding place!
i have kept black ghost for years now and found that they are a hardy specie once you satisfy those basic requirements