It is not skin but a dense mucus layer. They shed it regularly. More so when stressed, less so when comfortable.
IDK. You have given only two pieces of info - that the fish sheds mucus layer and that it sits still all day.
The mucus shedding is normal when done once a day or a few times a week. If multiple times a day, it may indicate a problem.
Sitting still is not normal for them but who knows, perhaps your lights are too bright, or the water is too hard / soft, the pH is too high or low or unstable, too low DO, too much current, perhaps there is bullying, or the fish is new to the tank, or the water has ammonia or nitrite, etc. etc.
oooh okay, he does it once a week or twice.
He is sort of new. I only have him a month or so. My Ph is slightly higher but not so high that I had problems with it. I only feed him once every 5 days. Can that be the case?
This shedding schedule I would rate as totally normal.
Feeding - IDK. If the LSN eats up a huge tummy, then it might be ok for 5 days... still could be a bit too long but you must go by the tummy - when the stomach returns from bulging to being flat, it's time to feed again. If you don't feed it or it doesn't eat till the tummy is huge, then once in 5 days would be starving it.
I feed my LSNs twice a day every day along with the whole tank but I have 18 and some eat, some don't, some eat a lot, some eat little, some take cut fish, some pellets, others both.