I was just reading online, and saw one site that said cuttlebones were a good source of iodine....don't know if they're right...so I would discuss this with a vet
It might do them more harm if they get too much??
When I got Jasper, the pet shop people told me to rotate through different brands of foods, as different ones offer different nutrients and different mixes of seeds. I give Jasper pellets, but do not plan on him eating mainly pellets. I add them to his seeds, and it definitely looks like he eats both. I put the seed in first, add a layer of pellets, and right now I top with some Quicko egg food as he is still molting. I saw an article once about the possibility of birds that eat only pellets actually getting to much of some vitamins and minerals, especially if they are also getting vitamin supplements. We all know they need fresh vegs and fruits...but do the birds know that? We all know how hard it is to get them to eat their veggies LOL
I've decided on a middle road approach, that's what I'm comfortable with. I've had parakeets before pellets were even available, and they were perfectly healthy and happy. My Charlie lived 14 years, she was just offered many different seeds, millet, treats, egg food, groats, greens etc. Different things, with lots of variety
Sorry, this got a little long............