I feed him two pellets in the morning and two in the evening every day, and fast him every sunday. (I'm pretty sure they're standard size, very small... I forget the brand.. I used to feed him Wardley Betta Food but those were a pain because they were too big for him to swallow, so I had to soak them and cut them in quarters lol)
Every other day I switch to feeding him two or three (depending on size) freeze dried bloodworms instead as his dinner. A general guide I've been told by numerous people to use is to feed about the size of his eye, because that's about the size of his stomach. So I think I'm feeding him well?
I remove "uneaten food" because he won't eat food that falls. Although his food is supposed to float, he typically spits it out once or twice then swallows it (if you watch carefully, he spits out smaller pieces, until it's all gone.. he also has done this with flake food). But the pieces sometimes sink to the bottom. He refuses to eat anything that isn't right at the top of his water... he's a very picky fish Lol.
I always let his water sit a full 24 hours in a similar container before using it btw when I do water changes. It sits right next to his cube on top of the heater so it becomes the same temperature, and then I use a water conditioner...