I just had one of my two Java ferns turn brown and seem to rot. I
have had this one in my tank for about 8 months. It is on a ceramic
arch, relatively high in my 55 gal tank. Initially, I had a lot of
leaves turn kind of black, I assume due to the intensity of light, 3
wats per gal, and that it was high in the tank. As my amazon sword
grew larger, it was partially shaded and seemed to do better.

I have another java fern, taken from the first, attached to another
ceramic cave, on the other end of the tank. This one is lower in the
55 gal tank, and sometimes shaded by the fast growing bacopa and
sunset hygro - between trimmings. It is just fine and a nice color of
green.

Possibility 1: I recently tried to trim some of the sword plant
leaves. I had always heard not to do so as it would cause the leaves
to rot. They haven't. But it has allowed less leaves resting on the
surface and more light to the e. tenellis, dwarf sag and other smaller
plants below. Could be now the more light it is receiving.

Possibility 2: I have been treating my fish for parasites.
Initially used Anchors Away - diflubenzuron and later Paragon II -
Metronidazole. The later I have done 3 doses. Some of the latter
chemical took a while to dissolve (I had dissolved in warm water as
much as I could before introducing it) and seemed to stay on the
surface, stick to the sword leaves on the surface - none of the fern
leaves reach the surface. But if it were the chemicals, why not the
other fern?

Possibility 3: Less water changes to allow the chemicals to work.

Possibility 4: I recently resumed PMDD dosing. Actually I am using
some Flourish samples I got at the Houston AGA conference. I also
added some Flourish tabs (small "stones") in the gravel; I previously
used "Root Tabs plus Iron" but my store was out of them. Used about 5
in my 55 gal which has pea gravel mixed with flourite.

Other plants seem to be doing great.

Same light duration; same fish food; no change in fish population.

Suggestions/ideas of cause?

Bob