I brought 6 Julii Corydoras home from my LFS yesterday, put them into quarantine, and fed them live bloodworms hoping to fatten them up before medicating. One had what I thought was an injured Pectoral fin and possible injury to his swim bladder. I put him into a separate nursery tank I was preparing that had already been medicated with Methylene Blue, hoping to prevent infection. This morning he had passed away, and I noticed that a few of the other Corys now had large portions of their fins missing and fraying. Other than the damaged fins, I have not seen any signs of the remaining 5 acting unusual. They are resting together in their shoal and traveling up to the top of the tank for air. I am guessing this is fin rot, but I have never dealt with this before with my livebearers.
The picture I added is the one who seems to be in the worst shape. His entire tailfin has completely frayed away. I have added aquarium salt to their tank at half the usual dose; although, I know there is conflicting information about how sensitive to it corys really are. On hand, I have the Quarantine Trio, Methylene Blue, API Aquarium Salt and Malachite Green. In the past, I have known people to use Maracyn 2 for Fin rot, but I can't find it anywhere at a reasonable price or that could be shipped to me in time. Will regular Maracyn work? Should I go get Malefix from Petco?
Water Parameters:
pH: 7.2
Nitrates: ~15 ppm
Hardness: ~200 ppm
Nitrite: 0 ppm
Ammonia: 0 ppm
KH/Buffer: ~40 ppm
Water Temperature: 79.1F