Strange Bolivian mask??

[riverlanddiscus]

I have 3 bolivians in my 4 foot discus tank. One of them has developed a dark grey mask that covers exactly half of his face, down to the beginning of his dorsal fin. It is not nearly half, but exactly with a perfect straight line from the tip of his face to the top of him. I can't find anything about through search engines, and thought I would come to you good folk. Everything else is as normal - eating fine, still chasing the 'young chick' around.

Ph 6.2
temp 29
gh 60
kh 10
no2 < .5
no3 20

I just need to know if it is a danger to my discus. I have a planted tank too.

[riverlanddiscus]

Here is pic - sorry not real clear.

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<a href="http://i225.photobucket.com/albums/dd79/ashmumoo/123003.jpg" target="_blank">
http://i225.photobucket.com/albums/dd79/ashmumoo/th_123003.jpg</a>
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[riverlanddiscus]

It would be if I could get it to work!

[riverlanddiscus]

here goes another try - if not, I am giving up. Yes I am a sook!

http://i225.photobucket.com/albums/dd79/ashmumoo/th_123003.jpg (http://i225.photobucket.com/albums/dd79/ashmumoo/123003.jpg)

[riverlanddiscus]

Yeah! The other side is a normal looking fish - can't tell he is the "phantom of the operatank"

[fishgeek]

nerve irritation
nerves control the ski pigmentation, the left and right side of the body have individual nerves controlling that portion
you fish ahs irritation around a nerve that originates at about gill height on the spine

goitre/other growth/injection/other physical trauma are all reported reasons

if trauma then it will resolve over a period of time
the pale grey colour makes me thing the irritation is not as bad as some