Is it halal to use a hair dye that contains ammonia because I heard it doesn’t let water reach the hair (not sure of scalp) so it would then make the wudhoo invalid.
Additionally, I would like to know if strands of hair allows water through, and if this is a condition for wiping over the hair in wudhu.
Ammonia does not affect the wudhu. What prevents wudhu is a solid layer above the hair.
If you mean by strand the “braids” then yes you can wipe above your braided hair. From forehead backwards, and from the hair at the end of the neck back to the forehead. It is not requested to ensure that your hands passed by every hair. You just do it spontaneously.