wait.... ( i apologize ahead of time in case i misread anything ) so ... u added the novaqua before you do the major water change ? cuz that doesnt help eliminate the chlorine or chloromine or watever ... barbs r especially prone to those chemicals , they r always the first to suffer first.... and sadly, once u notice something is happening, its already too late.... and to fix the water immediately, u can overdose amquel ( except u have to make sure there is enough air since amquel does lower air level ) and add activated carbon immediately cuz that'll "suck" in stuff