a couple days ago one of my flying saucers leaves' started to wither, two days later it was essentially dead (it was the runt of the group and the rest in the same pot looked fine, so i just figured it was nothing much to worry about.)
this morning i checked on my babies, and one of the stronger ones' leaf is wilting,

and another one the tips are starting to turn brown-ish (i can only assume it is about to wilt).

why is this happening, and how can i stop it?
the only possible explanation i can come up with, is that they are over crowded? (the two plants pictured are in the same coconut half along with a third plant)
it seems to only be affecting my flying saucers, my heavenly blues are looking very healthy and growing strong.

p.s. sry for shitty quality. outdated cell fone is my only camera.

EDIT: also i use miracle-gro liquid houseplant food.
i add 3-4 drops of it every time i refill my mister/sprayer with water (the approximate amount of 1/2cap per quart as per directed, erring on the side of caution)
and i water these plants constantly.
could i be over-fertilizing them?
i only added one drop this time just to be sure.