I have a 3" clown and just bought another clown and it 1" 1/2 and wanted to pair them up. I want to know if i should still keep him in the tank because the clowns swim together but some times the big clown attacks the small clown.
The 1.5" clown could possibly have morphed into a female in the tank you got it from. Granted it is smaller than the 3" (most likely female) that you already have, but that doesn't mean it wasn't the largest, most dominant fish in the tank it came from. This would mean that it might have gone through it's dimorphic change already.
If you do have two females, then it would explain the aggression. However, if you did happen to get a male, then they might just be establishing their rightful heirarchy in the new tank setting.