You cycled the tank with the tomato, so now he is dominant in the tank. He established that as his home. Different clown species don't get along great usually anyway, but the tomato is looking at the perc as an intruder as he was added later. You may not be able to get them to play nice, but you could try rearranging the tank. That may displace the tomato enough to help. If you want both, you may want to try that first before taking one back (unless they are killing each other in which case don't wait).