Had to add a follow up on my Midas.
I thought I had a puppy dog who was easy going. I was wrong!
Last night I decided to get my red hook silver dollars before I had my new 120g set up. These were going into my 65g (36x18x24) growout with my 5" Midas. These SD's were 3.5", pretty good sized fish for my Midas. As I floated the new fish my Midas was attacking the bags, but stopped after a few attempts. So I thought that it would be OK to release the red hooks into the tank. After a few moments the Midas was biting the sides of the fish and attacking them! He nailed a couple pretty hard and I thought they were goners. This morning I awoke and found everything was just fine and he had accepted his new tankmates.
I learned a few things:
1. Dont let the puppy dog looks and attitude make you think your agressive fish is easy going.
2. Rearrange your tank before adding anything new, to give them a fighting chance.
3. Sometimes it is better to wait to add new fish - I really could have held out for two weeks till my 120 was set up!
But in the end it really depends on your fishes personality.