SillySnail, this thread is more than 2 years old. It's better to start your own thread than to resurrect old ones. :)
I strongly suggest reviewing your care arrangments for your betta. If you are basing cleaning on visible dirt, that is not a good idea. What harms fish is ammonia, and that is invisible. With a mystery snail, which has a huge bioload, and a betta in a half gallon tank (not an ideal home due to the lack of water capacity and the inability to heat it) you should be cleaning at least every day, because trust me, your ammonia levels are skyrocketing.