Sounds like fin-rot which is a fungal infection, and again is very often a symptom of poor water quality. Without test results to confirm it, I think it's reasonable to assume that the Cycle didn't work, and that you are in a fish-in cycle situation, in other words you are using fish to provide the ammonia to grow the bacterial colonies in your filter.
Reading the green link in my signature area will help you greatly, but you need your own test kits to know exactly how well the ammonia and nitrite is being processed. Most people on here will recommend the API kits, although I am going off them, because it's often difficult to tell the low readings on the ammonia kit. I use the Salifert kits myself, but also found the Nutrafin ones easy to read.