Can a fish get a disease if there is no disease in my tank?

[kilofey]

I'm not sure what's going on with my six line. He was quarantined for 2 weeks at the lfs and has been in my qt for about 3 weeks now. So a total of 5 weeks in qt. He has been healthy and eating like a little monster since I got him.
I switched my qt from a 5 gal to a brand new 10 gal last week and put lots of LR in there to ensure I don't get an ammonia spike. Water tests out good: amm 0. Trites 0. Trates 10. Sg 1.022. Ph 8.4
I think he scratched himself on a rock during the switch, but instead of getting any better, it has spread to the other side of his head. I don't know if its red or not cause he has a naturally red face. Could he just have scraped himself on a rock on the other side or is it infected and if so, how do I help him? Its not white and fluffy but he does have little white scratchy looking lines on his head.
I don't know what to do cause I'm leaving for Kentucky on tueseday for a week and my boyfriend will be left taking care of my fish (which makes me nervous as it is even if my fish was OK).

 

[beth]

Can you post a picture of the problem? Is the fish eating and acting normal?

 

[kilofey]

I've been trying to get a pic of him all day but he's not having it. He's too quick. He seems normal, but he hangs out in a hole a bit more often and he does eat normal

 

[beth]

Is he eating? Is the wound area red, getting larger?

 

[kilofey]

Good year, the six line died last night I don't know what happened I guess his injuries were too severe. Maybe it was red but I couldn't see it cause his face is normally red anyway. Well, I guess ill try some pimafix and melafix as a precaution just in case he was sick cause I don't want U-boat, my bar goby to catch it. At the moment, he looks great and is very active and eating well. So hopefully he will be okay :sad:

 

[beth]

Sorry for the bad news.