Plant disease !?

[Roger Miller <rgrmill at rt66_com>]

Folks,

I'm writing to relate a story of the bizarre.  Well, bizarre if you really 
don't get out much.

Last week I came home from work one day to find that one of the 10-gallon 
tanks in our dining room was a little cloudy.  A closer look showed that one 
of the cats had tipped over the yeast CO2 bottle and the tank took some of 
the solution.  The fancy male guppies in the tank were all either dead or 
dying.

I moved the surviving guppies, but most of them died anyway.  The yeast 
didn't seem to effect the ghost shrimp.  I did a very large water change and 
left the tank empty of everything but plants and shrimp for a few days.  Last 
Sunday I did a regular ~30% water change and did some plant trimming.

The tank grew a prominent grove of dwarf lobelia that occupied about 2/3 of 
the floor space, plus some E. tenellus, Crypt. moemanii, Potamogeton gayi 
(thanks, Tom) and a Limnophila sp.  The lobelia gets too tall and now and 
then I pull it up, trim off the bottoms and replant the tops, which is what I 
did on Sunday.  The water was clear and everything looked ready to 
reintroduce fish.  I didn't reintroduce fish, it just looked like I could.

Wednesday I noticed that the lobelia was looking a little odd and then on 
Thursday I could see that the lower leaves were dark.  By Friday night I 
realized that the dark leaves were dead.  Only the young leaves near the top 
of each plant appeared to be alive.  I also noticed that the small Quick 
Filter in the tank was completely clogged, only 5 days after a thorough 
cleaning and bleaching.

Saturday morning I finally had time to look into the mess.    It appears that 
every one of the dwarf Lobelia -- probably 25 plants -- was dead and rotting 
from the substrate up.  The substrate is onyx sand over about an inch of 
aquarium gravel.  I removed everything that didn't turn immediately to mush 
and replaced the Quick Filter insert.  The old insert was still white 
everywhere except on one end and completely clogged with lord-knows-what.

All the other plants in the tank look completely OK.  The only thing I can 
figure happened is that the yeast incident boosted some potential pathogen, 
which then invaded and destroyed all the lobelia at the cut end of the 
stems.  I've never heard of such a thing happening in an aquarium.  Has 
anyone else seen this happen?

Roger Miller