I agree with the PraziPro and, IMO, all fish should be treated for internal worms. It's so mild that's there's no reason not to use it ...especially in new fish. I have read that garlic food may help prevent worms but not get rid of existing worms. Not sure if that is accurate or not but it kinda makes sense to me.

Mountain Discus, a breeder that sells on the internet, also recommends Omega One fish flakes for their Discus. It's made of real salmon. They feel fish pellets are not as good for them due to their flat stomachs.

Do you think perhaps this fish may be bullied and the others not allowing him to eat?

I would not use the melafix. Gosh, King Fisher is right on. Turn those lights off. They need not be on over 8 hours a day.