Im not going to attempt to answer this quetion for Brian but he has answered it for me in the past with the reasoning why, so here it goes.. The idea behind having a growout tank for juvi. discus is the fact that juvi. discus need alot of water changes, more so then adult discus, and the smaller tank makes the water changes smaller and if for some reason they need medicated there is alot less water to maintain.. And if you start with a smaller tank you will have to move them to the larger tank sooner, proper acclimation is a key to keeping discus and maintaining the same water longer will be easier to keep them from becomming stessed.. Hope this helps