Need more info. ESPECIALLY your medium. If you just
flush your plant with ph 8 or so water until your run off hits about 6-6.5
and you're in soil...great. If you're in coco, you're hosed. Coco's ph range is different from soil's.

Also, there is a reason it's nose diving. If you don't find out what that is and fix it, you're gonna be back here in two weeks asking the same thing.