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Mysterious Cory Catastrophes


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On 9/25/2022 at 4:15 AM, nabokovfan87 said:

Not sure this fits.  What Colu mentioned might be on target. 

Fish are stressed, tired, low oxygen (comparatively) and then you add a powerhead.  They rush to the surface to get air, sometimes, and because it's a tall tank it can be stressful on an already stressed corydoras.  They smack the lid, causing internal damage.  It happens.  Happening to every fish isn't likely but if you're keeping the waterline near top of the rim, I can see it happening.  Then.... fish are trying to hold on and keep going and you add a powerhead.  Stressed fish, under more stress because of the added flow it needs to swim against.  The photo you showed had a cory with it's tail almost 30-50% completely gone.  That fish had some pretty severe issues to be in that shape, whatever the cause of it.  I can't speak to what the others looked like, but whatever is the cause of all these issues there's a few things I would highly recommend doing right now.

1.  Add an airstone if you can.
2.  Add a feeding dish for corydoras with this gravel
3.  If you can, if you don't have a risk of killing plants, probably add some aquarium salt.
4.  Treat with general antibiotics like Colu mentioned.
5.  Treat for fungal with Ich-X and follow the directions on the bacteria medications.  If it says to change water on the third day, you'd change the required volume and re-dose with Ich-X as well as the bacterial meds.

Because you're having such severe issues, I would highly recommend having a QT tank setup and use it on any new fish you purchase.

Thanks for the thoughts. 

I had never seen them darting to the top for air - my tanks are on each side of my TV so I can notice if something strange is happening.   Water is 1 inch below bottom of rim/ 2 inches from top of rim.  I have not see them trying to swim against the flow, or struggling to swim.   They have stayed towards the front of the tank and inside the decorations.   Lower powerhead is is pointed along/against the back wall and slightly down so it helps flush the detritus towards the intake.  I have the same setup in the 55 gallon with angels where flow can cause them to fatigue and die due to constantly fighting the flow and they are all fine, as are the spotted cory.  There are no more cory's in the 36 gallon at this time, so waiting to see what else happens.   I do have live plants.  One thing I forgot is that I had the infamous brown (diatom) algea bloom so I was making sure to vacuum gravel more to get that out/off the gravel but everything I read does not state anything about affecting fish and my plecos are fat and happy. 

On another forum, a moderator posted this .....

"This unfortunately is quite a common problem in corys, it tends to be known quite simply as red blotch disease.
It's not known exactly what causes it, if you catch it early enough you can try treating with a broad spectrum antibiotic.
Panda corys seem to be a lot more delicate as they're so intensively bred now"  

So, just going to let this sit for a while and see if things level out.  FYI, I do have, and use, a quarantine tank.  I have looked at any new fish with a critical eye before even taking them home.

FYI - lone panda I moved to 55 gallon - still alive and kicking.


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On 9/25/2022 at 10:17 PM, Mitch_ScruffyCityAquatics said:

I think adding an air stone could help. 

I believe 77 degrees is toward the top of the temperature range for pandas… is it possible to drop it a couple of degrees without bothering the other inhabitants?


On 9/25/2022 at 10:17 PM, Mitch_ScruffyCityAquatics said:

I think adding an air stone could help. 

I believe 77 degrees is toward the top of the temperature range for pandas… is it possible to drop it a couple of degrees without bothering the other inhabitants?

Yes, 77 degrees is at the top of the temp parameters, but doesn't seem to affect the spotted ones in the 55 gallon.  The temp of my tank(s) is affected by the ambient temperature in the room.  Both tanks run within a degree of one another.  Currently, the 36 gallon is at 77.7 degrees and the 55 is at 78.3.  The cory's were dying even before I added the powerhead.  The powerhead at the top/water line is there to break surface tension and allow for gas exchange.  The lone panda that was in the 36 gallon and I moved to the 55 gallon is alive and well and eating and it has been over 48 hours.  It is definately something in the 36 gallon that is affecting the cory's, or at least the panda's, and I am beginning to believe what a moderater stated in another forum.   Like I said,  the only difference between the tanks is I have 2 ornaments that I ordered from Amazon that I rinsed good before putting them in that tank.  If I take them out, my plecos are going to be none too happy but may come to that and I will have to make a cave for them out of natural stone.  I may also buy 3 spotted and put in that tank and see if they also die/come up missing.  That way I feel I can say it is something in THAT tank and go from there.  Just funny that the tetras and pleco are not affected.  



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