Well I have a dirty secret I will share. I have a blue hippo and I purchased him when he was a inch and a half in length. I put him in a 55g for a year. Next year, I added another tank which was a 90g tank. The following year I purchased another tank 125g which he is currently housed in. Currently he is 7-8inchs in length. It's almost time to upgrade the tank again. So I'm thankful that I purchased this fish and upgraded along the way. My better half allowed me to keep each tank.

lol
Essentially what I am getting at, don't purchase a fish with the intention of getting rid of it when it's to big. That's not fair. How would you like to be traded to another home when you are 16 years of age? Do you know what I am getting at? We (Reefers) are essentially their "god"/"maker". It is your job to ensure your kids are doing okay! If you can't take care of the kids properly, don't have kids.