I have had literally 10 die on me in last 2 weeks. I sent my water to PETCO for testing and all the levels are fine, nobody knows what the problem is. after a while the Barbs will go to the type of the tank circle around, like they are sniffing the top of the water but they are actually gasping for air. they do this until they eventually end up dying. I put an oxygen pump in there as well and its still no hope.
I really want to get more cause those fish are awesome and a blast to watch but I am not trying to have anymore die. its mind boggling.