Why wont my betta fish eat?

Brief：
I bought him a couple weeks ago and he was great! I change his bowl every week like Im supposed to, but now hes not eating, and his colors are going. .. 

I bought him a couple weeks ago and he was great! I change his bowl every week like I'm supposed to, but now he's not eating, and his colors are going. I'm a little worried. Am I doing something wrong?

Are you feeding him brown pellet-like food? Live food? Freezedried? And did you get him from a petstore?

I know that a lot of pet stores pretty much neglect their bettas, not feeding them daily and never cleaning their bags/jars. He might be sick, maybe buy some maroxy and add a drop to two, I feed my bettas the best bloodworms I can get my hands on, 3 times or more a day.

He could also be dying, I am sorry, but my betta stopped eating a day before he died. They seem to do that. I hope this helped.

To Princton_Girl: "betta fish are very short lived fish. i myself went through 2 myself. they are die quickly and when they stop eating the food they are sick. if you clean the bowl and add food. check to see if the food is eatten and also they poop. if they don't eat the food and poop that is their guts. these fish get sick pretty quickly. try putting a water plant over the bowl. the kinds that people buy with the beta fish that come with it. they eat the roots and breathe from the air in the water. the plant constantly adds air. "

DO NOT Do what she says. The vials with a plant in it is like a TORTURE CHAMBER for your betta! They do not eat the plant, they are carnivours! They don't breath the 'air' from the plant, they need real oxygen in the air. And the plant DOES NOT keep the bowl clean! Give it some time. I have one too. Are you feeding him the special Betta food? If so, he could be sick. There are wide-spectrum curatives you can put in his water if he's sick, and you don't know what's wrong. No you aren't doing anything technically wrong. He may be sick or maybe he just doesn't want to live anymore. Give him attention! I use to have one and whenever i played the piano my fish got very happy. So maybe like talk to him?