I've had some of the barbs for at least 6 months. they lived in 4ft community tank but when I decided to get lyre tails I knew I'd have to move them. So about 3 months ago I relocated them to a 2 ft tank that had been set up for over a year. I do a water change and top up regularly (weekly) at @ 25%. I check amonia, nitrate and ph levels usually monthsly but when the fist one died I checked and kept checking levels, but no change... only added cycle and aqua plus when doing water... no other medications. The dead fish haven't seemed to show anything physical but I must admit I didn't look with a determined eye.. just noticed the body and removed. I ddi notice that a little one before it died seemed 'shy' it hid to the back of the tank all the time. Normally they tend to be all over the place. Feeding - once a day with Nutrafin max for tropicals. they occasionally (?weekly) get an alge wafer (the bristles love it but so do the barbs)....
thanks for the help....