Depending on the size of the atf, Id say get him to about 6" then start getting him off live foods and on Market Shrimp, Freeze dried Krill, Beef Heart, Crickets, pellets... etc
As for Temp, if you want to grow him out pretty fast, I would bump the Temp to 87* and add a powerhead to the tank (I would face the powerhead and the return of your filter the same way).
Very important... If you bump your Temp up, make sure you have a lot of air. The air in the water gets thiner and you may see your fish surfacing more
Just my 2 cents