Help! My Pleco Has A Weird Wound?

Hi, I am very new to this forum, I come seeking help.

I have a tropical tank, with perfect water perimeters. The tank houses; 5 Platies, 5 penguin tetras, 5 cardinal tetras, 5 Harlequin Rasbora, 2 clown loach, 1 Black red tail shark and a plecostomus.

The Pleco is slightly too big for the tank, although lives comfortably under a artificial log with the shark. She only comes out during the night to feed and moves around with out an issue. We have had her for around 9 years give or take and has stayed at her current length for the last 4 years.

two days ago, the pleco was startled when I cam home from work during the eve and she knocked herself on the log, since then she has developed a strange marking on her face and I am very worried.

Here is a picture of her injury, I am keeping a close eye on all my other fish for signs of infection/disease but they all appear perfect and happy. Its not effecting her eating habits or how she moves around.



Uploaded with ImageShack.us

Has anyone seen this before and can anyone suggest what I can do to help heal or treat it.

Many thanks

Lucy