I put (2) blue's in my 500. At the time they were the size of a dime. One grew faster, they became about 5" and 6". The larger would chase the smaller around the tank. One morning I found little blue on the floor behind the tank. I had him almost 3 years, it was a sad day... They have their own personally, grow to know you and big blue will eat out of my hand and let me pet him... Now 3 years later big blue is almost 10" now, fat and sassy..
Happy Reefing