Just because frags are swapped from one domestic tank to another, does not negate the need for a quarantine tank. I haven't read anywhere that you guys are QT your specimens from other people's tanks for 3-4 weeks then adding it to your system. I think it only makes sense that if you don't want other people's; strains of resistant algea, flat worms, reb bugs, etc, it would make sense to QT everything you get for a while!
What could happen, especially at these local frag swaps, is that everyone's tank could be infected with the same harmful organism and wipe out everyone's tank in the area. That wouldn't be too much fun.
I would strongly suggest everyone set up QT tanks and then participate every other month in a swap rather than monthly. Because the desire to get your new aquisition into the display would force you to either put a new specimen into the QT tank, or move an old QT specimen into the display too soon to make room for the new aquisition.
Anyway, sorry for the losses, but that's my .02
Oh yeah, and none of this may be any of my business since I have never participated at a frag swap. It does sound fun, I just don't have anything to frag or swap
