This is because most Flowerhorn get increasingly aggressive as they get older. You will see the best from your Flowerhorn, with less potential problems for them (and other fish), if you keep them solo.
My Kamfa resides in a 5' tank solo; this is a reasonably good size for an adult Flowerhorn, though of course 6' would be even better.
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Agree with others... You can attempt tankmates, but if the flowerhorn grows large a 5' tank will start to look smaller and smaller, and the FH may not want to share it. Depends on the personality of the fish. I would say give it a shot, add 3 or so fish at once, not one or two, and keep a tank divider on hand in case it goes wrong.
Beautiful setup
I would keep it solo, chances of successfully mixing it in a 5ft tank wth BP’s will be slim to none.
Thanks a lot. I will try but not sure. A tank divider idea is awesome. I think even if I won't have troublea initially but maybe later it can be problematic. I kept mbunas and some of them were timid when small or new but then use to chase every other fish to death. I think I ll keep FH alone if I decide to keep him.
Islandguy11, your fish is gorgeous. Very beautiful.