You have a very large number of fish in there. The Tiger barbs grow to 3", so the tank will be overcrowded as they mature.
How often and how much do you change with each
water change? How long has the tank been set up, and did you cycle it completely before adding fish? Did you put all the fish in at once?
You say they look like they're shedding, and that makes me think perhaps they ARE shedding their slime coats which could be caused by high levels of
ammonia in the tank, which burns the fish and can cause what you're seeing.
You really need a
test kit. In the meantime, I would start doing water changes asap.
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