Java Fern question

I have a bunch of java fern attached to some driftwood.  
It has been in the tank for about 10 months now and was
florishing.  All of the sudden, the leaves started to turn
black.  I pulled the a majority of the leaves off, leaving
1 or 2 that looked healthy.  

The tank is a 55 gallon with 3 48" bulbs (a mixture of tritons
coral life, and perfecto).  The ph is 6.8, kh is 3, and gh is 6
with C02 injection.  I also fertilize with ferovite, laterite,
and Tetra Florapride.  

I also have some frogbit floating above the java fern, but this
has been there for the full 10 months.  Java moss is also growing
on the same piece of driftwood and is doing fine.

Any suggestions would be greatly appreciated.  Thanks in