Cory Illness


New Member
3 May 2017

We have a Cory which looks like it's mouth is rotting away! It started with a small white spot on its nose and has been getting worse. We have treated with Melafix and Myxazin but now the fish looks like in the image attached. I am not sure we can save this one as we have already lost one this way so we're worried it could be something contagious so wondered if anyone had any ideas what the issue could be?


We have 5 of the cories along with several Lemon Tetras, Cardinal Tetras, Ottos, Shrimp and an SAE. The tank is 120l and has been running several years. We have had the Cories for a couple of months and the other fish for longer. I tested the water at the weekend and it showed pH at 7, Ammonia & Nitrite 0, Nitrate 5 and the kH was 5. The temperature is 24.

Thanks for any help.
26 Feb 2013
Yes, it is bacterial looking and the culprit could be the gunk sinking in the gravel.

I would not change the substrate now, as it will shock the water quality but I'd clean it well with the siphon. Long term, replace with sand.

As for the cory, treat with a med that claims to treat columnaris.

Simon Cole

25 Dec 2018
To be honest it's gone too far to treat. High copper concentrations will gradually kill the corydoras. Something like nitrofurazone might work but I am pretty sure that it is regulated. I have never known anybody to successfully treat columnaris. There is a chance it could be another pathogen. Personally I would change the substrate and I would use potassium permanganate to sterilise the tank, before rinsing it away and replacing the fish.
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