In addition to removing the flowerhorn, you could try adding more cover and uping the hiding spots to 6 or 7. The more easily accessable places to hide the more a fish (especially fish that are preds) will be comfortable. Even "screens" of weighted fake plants would help for the time being... at least until they are large enough to shred them .
If that still doesn't cut it, try some dither fish. Some fish, and larger Cichlids in particular, guage how safe their surroundings are based off the activity of other fish. When there are no other fish, sometimes they go into "it's not safe" mode and become skittish.
Dithers can be large Giant Danio's, any of the larger (less expensive) rainbows or anything else that's fast, doesn't get HUGE (say maxes out at 3-4" give or take), schools and is relatively inexpensive. They may get picked off every now and then which is why I say go inexpensive.
Chris
If that still doesn't cut it, try some dither fish. Some fish, and larger Cichlids in particular, guage how safe their surroundings are based off the activity of other fish. When there are no other fish, sometimes they go into "it's not safe" mode and become skittish.
Dithers can be large Giant Danio's, any of the larger (less expensive) rainbows or anything else that's fast, doesn't get HUGE (say maxes out at 3-4" give or take), schools and is relatively inexpensive. They may get picked off every now and then which is why I say go inexpensive.
Chris