Rainbow with big white spot on belly

[Bacms]

Just noticed this morning one of my red laser rainbows is doing poorly. Seems to show signs of clamped fins and has a big white spot on it's belly. Can't really see any other spots so not sure whether it is white sport. Also a slightly raised scales. Can't really get a good photo of it unfortunately.
Probably something related to stress has there was something wrong with my tank last week, fish weren't active at all for a couple of days, probably CO2 related but cannot be sure has pH was the same.

Any idea what it is and what I can do about it?

 

[Bacms]

The best I can do photowise

 

[Tim Harrison]

The sticking out scales are often a sign of Dropsy, which is not a disease in itself but rather a symptom. The scales stick out because of swelling due to a build up of fluid in the peritoneal cavity http://badmanstropicalfish.com/fish_palace/tropicalfish_disease_identification.html#Dropsy
Fish sometimes also get tumours, lesions, growths or cysts which could be a symptom of an underlying oncological condition.
If they are large it's unlikely to be the result of a parasitic infection like whitespot. For instance, a couple of my ancient neon and cardinal tetras have a single white cyst on their flank and don't seem any the worse for it, I just put it down to old age.