congrats on hitting over 1000 posts!!!!!!!!!!!!! (ken yirbu)
i did try to fast, but didn’t make it. usually on yom kippur and t’ be’av (at least till chatzos) i do fast the whole thing but i do test every two hours. if i am below 100 or rapidly going down i will suspend the pump. i also decrease my basal (like mosh3 said he does). but as a teen i did not fast even on yom kipper (if i had to eat i would eat less than a kezayis every 9 minutes)
i also have to learn to take a drink of sugar when i have a low and then wait about 15 minutes for it to react. if not, i will eat the whole fridge which of course causes me to go high. tough cycle.