What's in your tank? When I put in a coffee mug that I thought was clean it ended up leeching a milky color to the water.
Also if you didn't rinse any gravel you bought in hot water for awhile that can attribute to the cloudiness.
Do you have a filter? You let it cycle before adding fish?
This should help clarifying cycling. It's a very important process.
Sometimes when you add fish into an already cycled tank it puts it into a mini cycle. Cycling, in short, is the process of growing beneficial bateria. If your bioload increased you will likely see an increase in BB and thus a "mini cycle".
I think that's the basics of it anyway. I'm sure someone more advanced will come along and assist. In the meantime I suggest reading through a few of the stickies.
I'm not sure if anyone is going to need most of this information but try filling out as much as you can. Every little bit of information (including pictures) is going to help diagnose what's going on.
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
What type of food do you feed your betta fish?
How often do you feed your betta fish?
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Have you tested your water? If so, what are the following parameters?
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?