Can you post a pic of him?
With mild cases of Ich I like to do the two cup method-I move the fish daily to a new clean dechlorinated container of water for at least 3 days past the last day I seen the parasite on their body
If he came in a cup you can use this and float it in his tank to keep the water temp stable.
With the 100% water changes every 3 days I am surprised that he has Ich. It is important to clean the gravel/substrate really good to manually remove the parasite from his tank.
The Ich will die without a host (Betta), however, they can also go dormiant in the tank until the fish immune response fails or a sudden temp swing- usually going from cool to warm.
You can't kill the parasite while it is on the fish without killing the fish, a slow increase in water temp (84-86F) can encourage the parasite to fall off and then the parasite needs to be manually remove by vacuuming
Aquarium salt 1tsp/gal can also help kill Ich if it is not a salt resistant strain, also the aquarium salt can be helpful in prevention of a secondary infection from the wounds left by the Ich when they fall off.
Really important to keep water quality tip-top....but by your other post it looks like you provide really good care for your Betta.
Last edited by Oldfishlady; 09-22-2010 at 05:39 PM.