Sick Corydoras?

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mark4785

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Just over a week ago I bought one extra albino corydoras for my aquarium to add to the group of four in the aquarium. The albino corydoras that I added turned out to have part of it's tail fin missing and it was relatively pale and still compared to the rest of shoal. Today, as predicted, the corydoras with a segment of it's tail missing became deceased so I removed it immediately on spotting it.
 
From today onwards I have noticed that the rest of the group of Corydoras were continually going to the water's surface for air every 30-40 seconds. For some reason, they are taking oxygen directly out of the air rather than obtaining it through their gills. This alarmed me quite a bit as I immediately thought that there may be a lack of oxygen in the aquarium, perhaps due to there having been a deceased fish in the water for possibly 10 hours or more. However, the CO2 drop-checker indicated that the dissolved CO2 content in the water was safe and the other species of fish, black neon tetras, were not hanging at the water's surface for air.
 
I decided to do a water test to see if another parameter was out of range and found that the nitrite level was between 0 and 0.25 ppm. Given the result, I immediately did a 85% water change and observed the behaviour of the corydoras afterwards. I noticed that they were not going to the surface at all for a good 2 hours and then all of a sudden they started the old routine of going to the surface for air every 30-40 seconds. If this wasn't perplexing enough, the next thing problematic issue I noticed was that the drop-checkers (I have 2 on either side of the front glass pane) were still indicating the same CO2 reading. The 85% water change should have turned the solution in the drop checkers to a blue colour, however, the colour remained green!
 
Given all of the above, should I come to the conclusion that I've gassed the fish and the filter sponge bacteria (nitrobacter and nitrosomonas) with too much CO2? I know filtration bacteria need oxygen too to convert ammonia to nitrite and so forth so the presence of nitrite would suggest that something has upset the filtration bacteria.
 
Anybody know why the Corydoras are still constantly taking oxygen directly from the air?
 
I'm sorry for your loss! 
rip.gif

Unfortunately I know nothing at all about Co2 so can't really say why what is happening is happening, but did want to say it's normal for cories to come up for air. Possibly not that often though.
Hopefully someone with more experience will come along soon and help you :)
 
Sorry for your fish. Maybe it brought something with it into your tank (Ich(like)-parasite for instance). So keep an eye on that.
 
It's indeed quite normal for Corys to surface and take some air, but if that's more frequent there indeed is something going on.
Are they swimming along the glass as well? Corys react on small changes in water  (adding ferts, changing pressure, ammonia, nitrite, more or less O2 / CO2). My big Aeneus will surface quite a lot during feedingtime (almost jump out then)  My other Corys don't show this behaviour. It's somekind of stress-releaser as well I think.
 
But what's causing the stress?????  If there is any ammonia / nitrite in the tank, the Corys often are the first "to notice" being lowest in the tank. 
 
I don't have a real answer at this moment, but please keep an eye on them (as you did) and keep us informed !!
Don't think bacteria will die of by a high CO2 level : The black neons would have problems then as well I think.
 
 
Cheers Aad
 
Thanks for both your replies.
 
In response to DoubleDutch: I thought I'd add that the black neon tetras did start going to the surface and gasping for air; their heads were titled upwards and they would not move from the surface suggesting the water had very little o2 in it. I also witnessed one cory stuck against the intake grill gasping as though it had not surfaced for air and had become confused.
 
I obviously got a bit stressed out knowing that the neon tetras were exhibiting the same behaviour so I removed all the fish and put them in a 30 litre QT tank, placed a heater in their, a o2 diffuser and placed a small pellet in for the cory's and some flake for the tetras. They eat it all and I witnessed no gasping or frantic up-and-down swimming which was happening in the tank I had removed them from.
 
I did 2 100% w/c's on the main tank and syphoned rotting plant matter out. I also took out some foreground plants that had leaves rotting lower down on the stem. I thought I'd get as much dead plant matter out as possible as I'm thinking that the amount of rotting material is using a lot of oxygen up and may have contributed to the nitrite level.
 
The output pipe in the main tank is tilted more towards the water surface so a bigger water ripple is created and I've stopped all CO2 injection (I injected co2 for the plants). Having made these changes, I've placed all the fish back in the main tank and the cory's are currently surfacing every 1-3 minutes while the neon tetras are not.
 
Unfortunately, if my efforts fail I will need to re-home all of the fish as I'm an undergraduate student and simply don't have the time for this.
 
Okay. The surfacing has now to do with stress I think. Please realise an O2 diffuser is nothing more than an airdiffuser !!! It will help with gasexchange, but will hardly bring in any extra O2 as thought !!!!
 
Keep them feeding a little for some time (more food = more pollution = more possible ammonia aso)
Don't ever clean the filter to much BTW.
 
Fingers crossed.
 

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