Java fern problem

Season's Greetings all.
	I'm having a problem with some Java fern in one of my tanks.  
I've been growing this plant for some time in various setups with 
consistently good results.  However the java fern in this tank, secured 
to a piece of driftwood is beginning to turn brown.  It seems to start at 
the base of the leaf and work it's way up.  I had this problem in one 
tank, snipped of the offenders and no more problems.  However, in this 
tank it seems to be a bit more persistant.  This tank has been setup 
about a year with several other species which are doing ok. (vallisneria, 
Bacopa carolina, H. Polysperma, Sagittaria natans, Anubias nana and 
salvinia. Tank parameters are normal with some nitrate, 7.5ph, moderately 
hard water, duplarit balls in the substrate and Flora Pride added as 
needed.  I'm thinking either alleopathy from some competeing plant or 
maybe a disease specific to Java Fern.  Any ideas would be appreciated.

					Ho, Ho,
						Miles Morrissey
						mmorriss at sophia_smith.edu