You might look into fermenting the pellets. It can cut down on food waste because they can't fling it everywhere. Supposedly it also makes the nutrients more bio available too, from being partially broken down. It's very easy to do. They may not like it at first but you can always put some dry food on top, or feed them the wet stuff at night when they are tired and ready for bedtime-- if they're hungry, they'll eat it.
If you are particularly worried about it, and your birds are at least moderately handleable, you can weigh them on a scale to see if they are losing weight
