Tiels are mainly seed eaters. I don't have as much knowledge with tiels as I do budgies, so forgive me if I let a false statement out.

Bailey's basic diet is a 1 1/2 teaspoon of Zupreem, 1 teaspoon of Roudybush Crumbles or Small (whichever size the store has in stock), and about a tablespoon of Kaytee Cockatiel diets. However, tiels in the wild all feed within one guideline: Variety. In the home or in the aviary, the bird will require variety. I like to clip dark green, leafy veggies to his cage. Broccoli seems to work best, along with bok choy. Carrots aren't the greatest to clip as they dry very quickly. I usually shred carrots and scatter it in the seed bowl. On occasion, I'll share crumbles of my whole wheat bread (bleached, white bread isn't as healthy). I'm also in the process of trying out baked goods and sprouts on the birds. If Bailey's been a good birdie, I'll give him a Lafeber Nutriberry (crushed). There's quite a bit of sugar in Nutriberries, so they're for occasional treating