Thank you all for your responses. I can't tell you how helpful they
were. It's 11:13 in nyc right now and I have just finished replanting
my tank after i removed that evil gravel. It certainly wasn't easy -
i've been working for hours. I really really hope the gh goes back to
what it was coming out of my tap water. I can only imagine how
terribly stressful this has been to the plants and have little
confidence they'll bounce back.

Currently all the equipment is running and i figure i'll take a water
reading tomorrow night and post the params. If tomorrow night I should
find gh has not wandered back to the 3dh range should I just chuck all
the flourite (which still has some gravel embedded in it) and rebuild
the tank? I guess this is a bit premature...

Thank you all for your responses. I'll let you all know what goes down
(or up).