diseased water sprite or crappy substrate?

[Erin Poythress <anang3 at yahoo_com>]

Hello--
I am quite new to the realm of planted tanks, and
about three to four weeks ago I put in my first
plants, two pots of Ceratopteris thalictroides, which
were doing great until about a week ago. I noticed
soon after a water change/pruning that one bunch had
come loose from the gravel and thought I just didn't
replant it properly. I replanted it and days later the
two biggest bunches were dangling again. I read
somewhere that this happens when the substrate is so
dirty that there isn't enough circulation, causing the
roots to rot, so I vacuumed the heck out of that part
of the tank and replanted. It's dangling again, and
the stems are starting to rot. Should I just give up
on this plant and start over? And what should I do
differently next time to prevent this? Note: I also
have Anubias nana in there that is doing fine. I don't
have fertilizer under my gravel, but I use Seachem
Flourish Excel and Flourish Iron to supplement. 
Thanks!
Erin  

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