Changing the water regularly, you still need to get the proper chemicals to take out the ammonia and nitrates, etc that are in your tap. I prefer Prime, but any of the tetra line that you can buy in most stores such as Walmart, work good too. Usually one drop per gallon or so. It's just a combination of chemicals used to neutralize the chemicals in tap water that may be harmful to fish. That will help out a lot.
Try soaking the pellets for a bit in water prior to feeding, see if that helps.. sometimes they are too hard/big and if you pre-soak, makes it easier to eat. Most fish do the whole spit-out game before actually eating. Also, if you changed food recently, he could just be being stubborn as well.. sometimes they can be picky and prefer one brand over another.
So, try water conditioner, buy a thermometer for tanks and see what the temp is, if it's too cold, it's not good.. should be 76-82F is the idea temp range. I don't know what else you could do.. does he swim around just fine, active? How many pellets are you feeding at once? Have you put up a mirror next to it? I know, obvious question, but just making sure since they won't flare unless they feel the need to defend.