I used to breed a lot of African Grey parrots and have just been asked what to feed to get the best results. I used to feed a good quality parrot diet with over 30 ingredients but low in sunflowers and add a pich of vitamin powder to this each day. Most important is not to over feed as they will look fine and go through all breeding signs but eggs maybe infertile. They should run out of seed half way through the afternoon.
I fed on average half a mug of seed per pair of birds a day which is not much. Also fed a small amout of natures harvest soak mixture ( a teas spoon per bird) as Greys are very bad at eating fruit but it shold always be offered. Also one palm nut per birds per day. As for calcium I gave 3 drops of liquid calcium in the water once a week and twice a week when breeding.
My birds after 6 months were put outside in flight to get fit before putting them back down to breed. At this time when I caught them I always check the breasts to see if their weight was correct, to find out if I was over feeding which is easily done.
I hope that helps a bit and please contact me if you have any other questions at all