What Is This Weird Looking White Stuff

Hello this is my first ever betta fish (I've only ever owned goldfish) and when cleaning out his tank today I noticed that there are these weird white round looking things on the bridge and on the roof. I have attacted a picture but can someone please tell me what it is. Thanks!

 

Do you feed betta pellets? Kinda looks like old food with fungus growing on it.

 

Could it be fungused leftover food?

EDIT: I should really refresh the pages I've had open for a while before responding

 

Looks like rotting food, I find it in mine when I feed shrimp pellets, I use a turkey baster to get it out.

 

That's rotting betta pellets. You only need to feed about 4 a day to the betta, with 2 pellets twice a day. You're overfeeding.