What are the chances I could add them together without them killing each other? I have a 600 gallon FOWLR that is 8' x 4' x 2.5'. I have a powder blue already that is in my qt tank. He is about 4 inches. If I was to try this, would it be better to buy a large achilles? I could possible get one of the large ones off of diver's den. I have another qt tank that I coul use for the achilles. Then I could add them to the dt tank together.