You can try Harrison's pellets, and definitely offer a chop mix of vegetables and fruits at least twice a day. IMPORTANT: If your bird is used to a specific seed mix/pellet - make sure you wean him over to the new food over a week or two. First day should be 90% old pellet, 10% new pellet, next day, 80% and 20% etc.
Example of daily fresh diet:
breakfast:
One tablespoon of - finely chopped kale, carrots, blueberries, jalapeno,brussel sprout, swiss chard - mix in a little bit of seed and crushed up raw pasta.
dinner:
One tablespoon of - cooked sweetpotato, cooked wild rice, cooked quinoa, cooked oats, mix in finely chopped green apple and fresh lentil sprouts
Rest of the day : 1.5 tablespoons of Harrison pellets
Foraging toys - roughly 4-5 hours a day - filled with nutriberries and seeds.
That could possibly be a part of it..but whether it cures that or not, at least your little birdie will be getting a good variety of healthy food ^.^
You can save yourself some time by pre-making a big batch of the chop mix, and freezing them in ice cube trays. That way you can just heat them up, and then throw in a few fresh things (I usually keep the blueberries, apples and sprouts fresh). You can grow your own sprouts easily - I take some lentils, wash them and soak them for 8 hours in water. Then drain them , cover them with a dark cloth, and water them every few hours. In a couple of days you'll get some fresh sprouts. Kiwi and my dog Milo loves them!!