Sterba Cory group slowly dying

Joe80

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Hello all

I had a group of 6 sterba Corys in my 125 litre tank. About 6 weeks ago one of them died, 2 weeks after that, another one died, and now I fear that another one might die as she is showing early signs. Each Cory had the same symptoms, I tried researching but have not been able to work out what it is that’s happening to my Cory crew.

The symptoms are. The first thing I notice is that the dorsal fin is split and jagged, then they become wobbly and have troubles staying level, then they start fast breathing. It’s lasts 5 days and then they die.
They all seem happy and are active, they interact with each and don’t hide. Until they start breathing fast. Then they become lonesome.

Water parameters
Temp - 25 - 26 degrees C
Ammonia 0ppm
Nitrite 0ppm
Nitrate 5ppm
Hardness 12GH
PH 7.6 - 8 ( depending on which ph range I test with )

I do weekly 40% water changes. Clean the substrate at the same time. I have lots of live plants, various stem plants, Java ferns, Anubis, and floaters, frogbit. I also have some Christmas moss on a piece of wood. I dose with seachem flourish comprehensive once a week. My stem plants have flourish root tabs. I have sand substrate. The roots tabs are pushed deep into the sand, then covered with smooth pebbles. Other tanks mates are 5 platy fish and 1 nerite snail.

I know that many believe that corys are purely a soft water fish, but I have looked it up on seriously fish website, and they say that sterba corys water hardness is 1 - 15 degrees, so that is still with in range of my 12 degrees.

Any advice appreciated
Cheers
Joe
 

Guyb93

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I had the same happen to a group of 14 bronze corydora ended up with half dead it was after I introduced a group of 7 to my 7 and one by by the died similar symptoms to yours I have no idea why I put it down to I was keeping differnt water parameters than there previous owner but that was just a desperate guess , I have no advice on how to stop it I was doing daily 50 water changes and didn’t help for me
 
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Joe80

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oh sorry to hear that. I started out with 4 corys in the tank ( moved from another tank I had ) and then about 2 months later I bought 2 more....from the same local fish store. I’ve had the group of 6 for about 4 or 5 months maybe longer. One of the original corys died first, a male, then a female, now one of the newer corys appears to have the same problem ( split dorsal fin ). They all appear to be fully grown.
 
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Joe80

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ok so I’ve been keeping a close eye on my cats, and they don’t appear to going the same way at the 2 that died. One has a slight split in her dorsal fin, but it actually looks better ( less split ) than last weekend. Time will tell. I‘be done a lot of reading about it and i don’t think lowering my PH at this stage is a good idea, my understanding is that it’s better to have stable ph, than changes in ph. A ph of 8 is a bit to high though. It wasn’t 8 when I first set up the tank.
 

the_lock_man

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ok so I’ve been keeping a close eye on my cats, and they don’t appear to going the same way at the 2 that died. One has a slight split in her dorsal fin, but it actually looks better ( less split ) than last weekend. Time will tell. I‘be done a lot of reading about it and i don’t think lowering my PH at this stage is a good idea, my understanding is that it’s better to have stable ph, than changes in ph. A ph of 8 is a bit to high though. It wasn’t 8 when I first set up the tank.
pH is a little high, really, but you are quite right, a stable pH is far better than trying to artificially control it, with consequent fluctuations.
 

mbsqw1d

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Any other fish in with them?

Agree that they could do with being in softer, acidic water, however I'm not sure that explains the split dorsal. What decor do you have in the tank? Pics and vids would be good 👍🏻
 
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Joe80

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A few days ago her dorsal fin was split, it is no longer split but still a bit jagged, so hopefully she’s getting better. She swims normaly. I’ve got 5 platy ( and a platy fry ) in the tank, they do get a bit excited at feeding time, often stealing food from the corys. Decor I have wood, pebbles and some slate that the java ferns grow on. Thinking about it they could bash their dorsal fins on a few things.

Here’s some pics, I can’t work out how attach video?
 

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Joe80

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mcordelia

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You can't upload video directly to this site, but you can use a video upload site like youtube or vimeo, and then attach a link here
 

Slaphppy7

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What kind of test kit do you use?
The sterbai don't look *terrible*, though their color is off, just a bit
 

mbsqw1d

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Keep a good eye on those platys at feeding time. Those corys look underfed with sunken bellies. And the dorsal fins look like theyve been nipped.
 

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