Filament barbs won't get killed. They're fast little buggers and max out at 6". I have 5 in a 135 with my pair of Festae and they're the only fish that have been able to survive. I've tried Tiger barbs, Congo tetras, SD's, convicts, and the kicker...I lost 3 full grown Roseline sharks ($25 each at 6") out of 6 one night and removed the others. I FINALLY found some Filament barbs a while back. They were kind of pricey, I paid $12 each for 3"ers but nothing can touch them and they don't sleep I swear. I've also had 2 full grown ones living with a jag for a couple years now and he hasn't been able to eat them.