behaviour change

Question
i have a congo african grey that i've had since he was 16 weeks old. he has always been very tame and friendly, at least he has towards me. he doesn't like my partner so much. he will be a year old in a couple of weeks and i have noticed some behaviour changes in him. he has recently become quite aggresive and started to chew at his feathers. i think he moulting at the moment but the preening is turning into destructive behaiour. he has started to bite quite often when he is being handled and i don't know what to do about it. i have been giving him calcium supplements and a vitamin supplement in case it was a nutrient deficiency, but he does get a very varied diet of fruit, veg, seeds and other pulses sprouts and grain.

Answer
If you're putting the vitamins in the water, let's stop that and not be trusting the sales pitches of such products ok?
 He should only be getting about 20% seeds (and no sunflower seed) with 80% pellets (any kind, any brand).  Fresh foods should be served regularly (obviously not included in the 80-20% mix outlined above).  Calcium needs to be received naturally through foods like dark leafy greens, natural cheese, yogurt, etc..

 It's excellent that you've caught the plucking early.  This is a young bird and there's a lot of lifetime to go; plenty to work with.

 There's a lot more about ideal nutrition and even how to address feather plucking and getting your bird to be more friendly toward your partner
  

http://www.4animalcare.org/birds.html