Cory Nearly Dead

[Blough]

I have four cory catfish, and recently noticed that some of them lost their whiskers because my substrate was too rough, so yesterday I changed the substrate to sand. My fish where netted and put into buckets while I changed the sand, and then poured back into my tank when I was done. Today I noticed that one of the corys without whiskers is now laying on the bottom of the tank, belly up. I was going to fish him out, when my sister noticed that he is still breathing, but barely hanging onto life. He is currently still in the tank with the other fish. I just looked in the tank, and now he is in a different location, still belly up.
Ammonia: 0
Nitrite: 0
nitrate: low (did a huge water change when I changed the substrate yesterday, can't imagine its very high.)
new additions: The substrate is new.
tank mates: three other corys (they all look fine) and a betta fish (he is fine too.)
chemical additives or media in tank: I have media from another tank in my tank right now because I completely destroyed the nitrogen cycle when I changed the gravel.
exposure to chemicals: none
 
He just moved again, and is now right side up. Is that a good sign?

He seems to be trying to swim around, but is doing it upside-down. It seems as though his belly buoyant.

 

[Byron]

There is not much you can do other than keep the tank quiet so the cory can regain his strength without additional stress.  If the other corys were acting similarly, I would be more concerned that something was amiss with the water, such as ammonia/nitrite.  But these test zero and it is just the one cory, so something with the nitrogen cycle is unlikely here.
 
As to what it may be, I would suspect the cory was possibly injured during the netting/transfer.  This is very easy to do, as these fish are highly susceptible to almost anything.  The net may have pressed on the fish during netting against the glass, or similar.  If it continues to have difficulty swimming upright, this is most likely the issue.  Another possibility is that it was simply stressed.  Corys do not like being netted, or moved at all.  Obviously there are times when this is necessary, but that doesn't make it more acceptable to the fish.
 
Byron.

 

[Blough]

Okay, thanks.

 

[Blough]

He is dead now.

 

[Munroco]

Aaaah, thats a shame.

 

[Blough]

another catfish is acting the same. I don't even know if he's still alive. The tank temperature was a little low today (72 instead of 78) because I accidentally left the heater off, but its still in the green range on the thermometer. Is this also because of the netting, or is it time to start worrying that there is something else wrong?

 

[Byron]

Are you still getting zero for ammonia and nitrite testing?
 
A temperature of 72F is not too low for corys, though it might cause problems if it was a fairly sudden,rapid change from 78 to 72.  But if the tank just naturally cooled down over time this should not be problematic for corys.
 
How long have you had the corys?
 
Diagnosing many fish problems is anything but straight-forward.
 
Byron.

 

[Blough]

My ammonia is still at 0, though nitrite is up to 0.25 ppm. I do a weekly water change, and its tomorrow morning, so I'm just waiting until then. I've had the cories since last black Friday. I'm really hoping that it had something to do with the stress caused by the gravel change, and not a disease that's in my tank that could still hurt my three remaining fish. I know this isn't really much to go on, but thank you for your time and concern.

 

[Byron]

Nitrite above zero is cause for concern, so I would suggest you are probably dealing with a cycling issue.  Corydoras are highly sensitive to ammonia, nitrite and nitrate.  Daily water changes of at least half the tank, even 2/3, until nitrite (and ammonia) consistently test zero.  Using a conditioner that detoxifies nitrite (Prime does, and Ultimate) would help.  And I would also recommend a bacterial supplement, like Tetra's SafeStart or even Seachem's Stability.  These do noit instantly cycle, but they do quicken the establishment of the nitrifying bacteria.
 
Byron.

 

[Blough]

Oh, I wish I had read that before now. Unfortunately another cory just died. I'm worried about my last remaining cory. When I changed the gravel I used filter media from another tank, and thought that it would be good enough. I guess I was wrong. I'm going to do a water change right now.
Thanks for your help.

 

[RainboWBacoN420]

This might seem like a dumb question, but did you wash the substrate thoroughly before adding it to the tank?

I'm sorry about your situation. What kind of cories are they?

 

[Blough]

Yes, I did wash it. When I thought I had rinsed it enough I rinsed it three more times, just to be certain.
They where Julli cories. The ones I lost where named Juliet, Julius, and Julianna. The remaining cory is named Julien.