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Possible Fin Rot on Julii Cory? Please advise on treatment!


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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


julii 2.jpg

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On 7/14/2021 at 11:05 AM, Colu said:

It's definitely a bacterial infection What I would do is add aquarium1 table spoon for 3 gallons and maracyn straight away if you can't get maracyn API furan2 or kanaplex is what I would treat with

Thank you! I have Maracyn and will treat right away. 

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  • 2 weeks later...

I am a similar problem with a panda Cory.  I have him isolated and treated with the above recommendation and he is eating and behaving normally.   The rest of the group seem to be fine.  How long can I expect it to take his tail fin to grow back? Should I keep him isolated I’ll til it does?  Thanks!

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