How often is it appropriate to include citrus (like orange) into my sun conure's diet?

I am not a vet. I understand that Vitamin C is excreted in urine so it doesn't get stored like fat soluble vitamins. I think once per week is fine because if he did get too much on one day there would be several days to balance it before another chance. There is also VC in Harrisons, though. They say as long as additional food is < 10% of his diet the balance of the pellets is not undone. The thing is that even Harrison's acknowledges that no pelleted food has everything. We just don't know all the things they might eat in the wild.