Disease?

[Stab]

Is there some strange disease out there that will not harm existing fish but any new organism being introduced to the tank will be dead within hours and with no obvious symptoms? I might have just hit a streak of bad luck but any new fish I have bought in the last 2-3 weeks "ceased to function" shortly after touching my water. I mean, even friggin feeders die off all at once! I could expect a bad batch but this has already happened 4 or 5 times in the row!

By the way, all paramters are fine, my fish are thriving (other than being hungry due to dying feeders), and I am always shopping for the healthiest specimens. Whats going on here?

 

[Tokis-Phoenix]

How did you go about acclimatising the fish to the tank exactly? They are more likely to die because of something like not being acclimatised properly, if you got the fish from an area with a very different ph to your tank then that could explain the deaths as you need to acclimatise fish to the tank for much longer when acclimatising them to a different ph.