A couple questions about my new Betta tank?

I have a 5 gallon tank for my baby Mario :), and it always looks crystal clear when I first set it up; I put a Ph tablet in, ammonia prevention and slime coat producer, I have a good filter, etc. After I do all that, the tank gets cloudy by the next morning...what's happening? Also, what are the signs of a happy Betta fish? I want to make sure Mario is content. Thanks.