Salt bath is the best ich treatment I have used on fish that it is safe for. Betta's are ideal salt bath candidates. Salt bath's are most effective for parasites, fin rot, and ulcers. If you can get that heat up above 81 degrees would be ideal too.
Malachite green treatments work good too, but dye your tank silicon green forever and the fish get pretty sickly looking during the treatment. Jeaninel gave ideal malachite green treatment. I have used Rid-Ich in the past with success, but had better success with salt baths for fish that can take it.
A combination of the two would probably be best.
What you described a few spots then go away is when you really need to watch out, because that is the precursor to the major outbreak. The only time the parasite is vulnerable to the malachite green or other medications is after the first few small ones fall off ans before the massive outbreak of babies comes.
If you do not use an undergravel filter and have substrate that you can boil, take it out and boil it! wash and scrub the tank with hot salt water then rinse it well. You really can not replace your filter media or the tank will surely mini cycle, but you should rinse it in some treated water (not tank water)
- Ich is a parasite Ichthyophthirius multifilis that looks like salt crytals on your fishes scales. un treated it is very deadly, also very contagious. Any utensils you use to handle sick fish should be sterilized before being used again. Ich is also and exception to the separate the sick fish for medication rule. you need to treat the entire tank if you have more than 1 fish in it.
Ich lives in the substrate mostly so cleaning that is your key!