Why does my Betta look so depressed and don't seem to eat?

got a betta for xmas and put him in the jar with the plant on top but he looked depressed and didn't eat so i bought a betta container they sell at the specialized fish store and he still doesn't eat and seem to be hanging to the bottom of the aqarium. I only use bottled water and changed water a few times because of food at the bottom. I added the liuid for ph and a very very little amount of bacteria killer since my aquarium is quite small. As well, his fins seems to be drooping, but he does move