how do i make betta stomach little smaller and which kind of thing that make the bowl clean what is it called

well first is your betta a male or female, when a female is ready to mate she gets big with eggs, and if they arent' used then they get absorbed into the body again it just takes time, and you can put you betta with algae eaters or other kinds of sucker fish, it's no to either of them and that should help keep the tank cleaner, and if there is a big problem with the water being cloudy that means you are feeding him to much and should cut back to as many pellets he can eat in a few minutes, i usually put the pellets in one at a time until they get refused.
Goodluck!

how do you mean clean? do you want somthing to clean up all the poo and exstra food or the algea that grows on the side of the tank glass?

both and that somthing that get rid of the chlorine or what kind of water should use for my betta