For ich I follow the parasites life cycle, depending on how bad it is as some fish that are healthy with strong immune systems, all I do is make water changes, with Bettas I like to do the two container method. I use two small containers and move them every day to a new clean container and clean the container they were just removed from. I leave the next days container empty until I do the switch so that any parasites will die.
I do this method for at least 3 days past the last day I could see the ich on them.
If it is really bad I will add aquarium salt 1tsp/gal along with the two containers and daily water changes.