repotted my spider plant in a larger container since it outgrow the one it was in. in a week i found that there are black strips along the middle of each leaf, basically dead cells... black dead tissue, however the leaf itself was fine even though the inside of it had a black stripe of death. i had trimmed it off the affected leaves, what is it? and what do i need to do, i also placed it in the west window, it used to be in the south window.