A few people in this post have used dividers, i swear by this method. I put a new fish on the peaceful side of the divider on their own & leave them there sometimes up to 4-5 weeks, all the time doing weekly waterchanges & maintance etc, then when i think there ready, i remove the divider while doing a waterchange, so while the fish are running around madly they dont realise the barrier is gone.
By that time all the chest beating has been done and they seem to just get on with it.
Try this method 'x3' i've had great success & hav'nt lost any fish since. good luck.
...Danny...