Well water, tap water, and bottled water can have wildly-varying pHs, among other things. I'd pick the well water, since it won't need to be treated, and stick with it. He should have more water changes, as oldfishlady said. Don't leave uneaten food to rot, or it'll foul the water even more. Make sure the water temperature is in the high 70sF. You can get a Tetra 50W heater that's tiny and cheap probably at Walmart or other similar stores, Petco, etc.
Try soaking his food in some garlic juice. That might tempt him to eat something. You can also add a few drops of juice to his tank as a general tonic. And..you might try a salt treatment? Search on this site for circumstances/instructions on how to do that.
Clean water, stable water parameters, warmth, good food, hiding places are the first things to make sure your fish is healthy, IMO.