Tetra Deaths

["Steven Maier" <stevemaier at ameritech_net>]

About once every week I lose a Serpae Tetra to a condition in it's eyes and
mouth. Its mouth appears to fill with a very white substance and then its
eyes and the skin around its eyes and mouth flakes. The progression of the
condition is rather rapid and death usually occurs within 12 hours after the
onset of the Symptoms. This only affects one fish at a time and at very
irregular intervals. One thing that I do notice is that the probability of
such an occurrence appears to increase When I prune. Is there any possible
connection here? The Tetras spend a lot of time in E. Stellata. Some of the
Eusteralis that I prune leave a stump 1/2 inch across. `

I seriously doubt this is a water parameter issue.
Any ideas?
Steve