I have a 20 gallon (long) tank with 3 corydoras (Im guessing they are Swartz corys) a small pleco (about 3 in), and 4 swords. gravel is a mixture of fine and small and smooth. I do a quarter water change each month, ph 7.0, temp stays around 72 degrees F. not sure on the ammonia/nitrate levels. I do have some live plants which may be java ferns (they were given to me by someone who didnt know what they were either- they were just passed down thru the family). I rinse out the filter cartridge when it becomes clogged until it seems to be beyond acceptable use. This tank has been running for about 4-5 years with no major issues. I bought the 3 corys together as I've had better survival luck when I buy them "with friends" and they have been living happily and growing for about 6 months now. 1 of them (about an 1-1.5 in in length) which I believe is a female has developed a black/maybe dark brown lump on it's pectoral fin. It is located on the front part of the fin that appears to be bone about center and it around a millimeter in diameter. It is not a spot as their pectoral fins are clear and it it raised like a bump. I have no clue what this is, but my cory is exhibiting normal behavior and eating habits. The other two are fine with no lumps. All of my google searches have been less than helpful. one site suggested it may be that she is carrying an egg around, but I was under the impression they do that with their pectoral fins. Anyone have some light to shed on this situation?