Rosy Barb - Sometimes As Though Shes Gone Bezerk

Can you tell us some more information, please (it saves me going back through all your posts  )

Tank size
Ammonia, nitrite and nitrate readings
pH and hardness (if you don't know your hardness, look on your water company's website)
How many rosy barbs do you have
What other fish are in the tank with the barbs
Added anything new in the last couple of weeks

The more we know, the more things we can eliminate.

Your tank is plenty big enough - it is quite a big fish and it would have been quite cramped in, say, a 100 litre tank.
There aren't quite enough of them (8 to 10 is the minimum number) but there are enough that the fish should not be very stressed.


Something you could try is not feeding the fish for 2 days, then give them daphnia, frozen or live. This is the first thing to try before even thinking about adding any chemicals to the tank. If the cause is over-eating/constipation, this should clear that.