If it's a lutino the bald spot is genetic and perfectly normal. I have a feeling, since you said that the other feathers are healthy, that your bird is lutino. Also, most Cockatiels won't eat Harrisons. Good luck... I tried to get mine to do it for ages and eventually gave up when all my other birds started eating it. Cockatiels are seed birds. It's a fact of life. (Ask just about anyone) The best you can do is get them a healthy mix of seeds and pray to the gods that you'll stumble upon a pellet that they like. Mine actually started eating the Zupreem natural and Zupreem garden veggie blend. Give those a shot.

I've had LOADS of experience with birds. It's my job AND my hobby, so any other questions I can help with too.

Haylee ^_^