I am by no means an expert but doing a search I found the common thing most sites said was poor water conditions.
"Frequent water changes a must to improve water quality"
Where are you at in Austin and better question are you honest? (got burned recently for $150) Asking because I have UV that is just sitting right now if you find enough info to suggest using one, I did not see anything that suggested it.

http://www.fishpalace.org/Disease.html#Finrot

Clif