i use to feed mine hikari pellets as a staple, mealworms, earthworms, roaches and brine shrimp as treats. he would also picked at the algae wafers and cucumbers i fed the pleco that lived with him.
To be honest, I think that tank is a tad bare. I would add a big root of bogwood, a few plants attached to the bogwood like Java Fern or Anubias, some really big Amazon swords protected from digging by some very large stones around it's base. A cave made out of large boulders for him to hang out in, and some darker gravel will really bring out his colours. You did say anything to make him happy ...
Heres an example of a great tank that your JD would love.