Hey Vu,
As Phil mentioned... I had a Powder Blue that broke out in Ich pretty badly. I checked out the ginger method, but decided to go another way. I basically just mixed up some DIY food and added Kent Garlic Xtreme to the mix. Then bumped feedings to 4 times a day, along with making sure Greens were also present for him.
I think the DIY mix I used was just what I happened to have on hand at the time... Frozen Mysis Shrimp, Krill, Spirulina Brine Shrimp, Some Formula 1 & 2 pellet food... probably some other stuff also... along with the recommended dosage of garlic. Blended it up, then froze it in a ziploc bag.
Basically my thoughts on ich are that a healthy fish will beat ich. I know there's people that swear by pulling the fish for Hypo/Copper/whatever, but I wouldn't do it with a Powder Blue... or at least save it as a last resort. As long as the fish is eating every time you feed the tank, and looks ok... as far as breathing and activity level. I would leave it alone, and let it fight it. That being said... I would get a Hospital Tank up and running just in case. That way if he would happen to take a turn for the worse you can transfer him right away for Hypo. (a Hospital Tank doesn't need to be anything fancy... could just be a rubbermaid bin with a heater, powerhead, spongefilter, one of those ammonia alert badges, and some PVC fittings... no substrate).
IMO ich isn't that big of a deal, just handled improperly in most cases.
As some others also stated, keeping your water params stable will also go a long way.
Good luck.