I have six cherry barbs that have been in my tank since May of 2008, over the last few days about five of them have developed what looks like fin rot, but on its tail fin only, my water parameters is all good, however I have been upsetting the tank a lot more over the last week or so and don't know if this might have caused a change that they don't like. I am unsure what to do. I don't know if age would affect them all at the same time so not sure what is going on.