WHY DOES MY SOIL LOOK LIKE THIS?

They never had this white looking stuff on the tops of soil. Kinda looks likes salt ? One pic is showing the white specks and second pic of other side of the pot that doesn’t have it but also less light (busher side ) 3rd pic is just of her in general lol ( today - day 32 from seed
Also I’ve been watering with sensi grow a/b every watering since sprout 4th pic is of tip burn , i checked them yesterday they had burnt tips but they just appeared over night even though I haven’t watered in 5 days ( today I’m watering

My guess...Back off the nutrients, plant is getting burned a little and likely salt is building in the soil which is why it looks like salt.