You've got enough light with a 4-t5 on a 75 if the bulbs are newer versus older. If you have stock bulbs in a lesser-priced fixture you might conside upgrading the bulbs to ATI. How old is your tank? Most everyone agrees 6 months is a minimum to let everything settle in regarding water parameters if all else is ok. If it's less than that it may be difficult to keep him happy. He'll move around. He'll hide under rocks. He'll shrivel up and inflate and he will move a lot until he finds that sweet spot to his liking. Feed him very small pieces of silversides, mysis, or even chopped, store-bought, raw shrimp. I keep several fresh shrimp separated and frozen for future thawing, chopping, and feeding to my rbtas. They seem to like the raw shrimp best in my tank. You'll get mixed reviews on how often to feed him, but I've found that a small piece once per week does well as he'll make most of his food from the light he receives.
Good Luck.
Bob