OK, i realized that stink is actually onto something. the surviving plant has had crispy leaves since that watering also, so it must be the stupid ferts...

ive heavily flushed the 3 with about 3-4 cups of water each so that a good cup or more drained out.

anything else i can do, since it is a bad soil for flushing, and i dont want to nuteburn AND DROWN the survivor by trying to flush it.