Its all a gamble whether or not a fahaka can be housed with tankmates... although most of the time they tend to get more aggressive with age, so just coz it works when they are young, doesn't mean they wouldn't turn on any thing put in the tank with them as they age...
PufferPunk had a Electric Blue JD if i remember correctly living with hers for a long time with no problems, then one day it decided to turn on the JD and that was the end of the JD... but i'm sure PP will be in here to show you pics if she sees this...