Did you quarintine the new fish before adding them? Ich and finrot are pretty common diseases, and if new fish aren't quarintined there is a large chance of them introducing the disease to your other fish. Although, finrot is not all that contagious--it is usually caused by poor water quality. What are your ammonia, nitrite, nitrate, pH, and temp readings? What size is the tank, and what & how many fish are in there? What do you add to your water? Sorry about all the questions, they will just help us figure out what may be wrong.
