Don't use the Melafix, this will harm your Betta if you do. I didn't know about it either but you're only supposed to use like 1/4th the recomended dose for Betta's because it can coat their innards and suffocate them.
What temp does the tank stay at? Also, it's okay if he doesn't show interest in food for a while. I'll tell you, my boy Remmy didn't eat for a month when I first got him and I offered food nearly every day! Just don't leave the food in for him, this will rot and cause ammonia problems in your tank :)
I would try to get some New Life Spectrum Betta Pellets because they have garlic in them which is really beneficial to Betta's. That or Omega One Betta Pellets, both brands are excellent in Betta nutrition, Tetra's food isn't really good because it has lots of fillers like wheats and grains. Betta's are carnivores by nature so they eat lots of insect larvae, so they need their protein but also a healthy supply of fruits and veggies!
Also Blood worms should only be fed on occasion, they have lots of protein but nothing else and will cause some bloat in your fish. It's also the equivalent to eating cardboard basically, so once a week is fine :)
Keep us updated to anything that changes.