It looks to me like your L191 has black spot, did it loose it colour in blotches or was it an all over fade? Can you see many tiny black pinprick spots?
Black spot is caused by a trematode worm parasite and, although it looks really bad, actually generally does little harm to the fish if treated. I've had it before on newly imported baryancistrus and panaque. A strong fish worming powder such as Flubendazole treats it pretty rapidly, but I don't know if this is available in sg. Fish wormers that treat it are normally sold as discus wormers, but I've used them for black pot on plecs and it works very well. So if you think it is black spot try to get hold of some discus wormer.
Hope this helps, Conrad