This reminds me of my old Flowerhorn. He lived peacefully with several other fish, then one night he snapped and I turned the lights on to 3 corpses (A black ruby barb, a female Cutteri and a a female Convict)
Dovii are off the charts with aggression, especially when you're talking about one that's near 20"s. He merely tolerated the Clown Loach and Pleco, once the Front was added (I'd go slap that guy that told him a Front would be a suitable tankmate for a Dovii that big) all bets were off and they were just a victim of his rampage over the new fish.