looks like fin rots .. just viewing form the picture.. one thing that i would suggest just from seeing your pic is setting your temp higher to 86+ and - 89degrees.. for that will help it burn its metabolism quicker and also will aid on fighting bacteria to heal quicker.. and remember to add some aquarium salt to help on electolytes.. well this is if you hadnt turned up that temp
goodluck
keep us posted,
respectfully,
vanz aka paintsn