There are 800 - 1,000 micron ones.. Brineshrimpdirect. com has some for future reference if need be. Your guy should still eat them.. I feed some of my larger adults NLS Grow formula which is very tiny.
The ones you got are rather small, why I recommended the larger ones.. but if you couldn't find them, then the ones you have should be fine.
Honestly, I don't count how much I give of food to any of my fish. I recommend numbers to people to make sure they don't over feed (and to not be judged). But I, along with many people who have raised/bred for decades just gets the feeling how much to feed each betta.
Just put a pinch in and see how it goes.. less next time if too much, or more if not enough, etc. You will be able to tell what your betta likes after watching him eat a few times.
Those are the only ones in the product.. unsure why exactly starch/grain is in foods - I have always assumed as "filler", and the grains more for digestion. The person to ask about why those are in the food would be Oldfishlady, if anyone knows, it would be her :)
Hey one more question about the GPs...If you don't mind...
I looked through all the Ken's fish foods and the GPs are the only ones that don't have some kind of wheat or yeast product in it. Are the ingredients in the description the only ones in the product? I thought pellets had to have some type of starch or grain in them to keep their shape. Am I wrong about that?
The 500-800 should be fine, just feed a bit more is all. In an airtight container with minimum extra headspace, in the freezer. This helps retain vitamins, slows oxidation, and keeps fats from turning rancid etc.
Forgot an important thing - Take a bit of tank water and presoak the GPs in it for a short while before feeding.. just a couple of minutes. Some claim the air releasing from it in the belly can kill. Haven't seen it, but better safe than sorry.
Also I would get NLS or something similar as well to mix in the feeding if you wish.. although GP is awesome and high in protein, it is a little low in fiber, other food mixed in the schedule will help on that. But overall, GP is still ideal.