Why are my cory cats dying?

[JCarnes]

I have a new tank, not yet cycled, and my cory cats are dropping like flies. I ended up with two apple snails, three ghost shrimp, a powder blue dwarf gourami, and one black skirt tetra after a family member had a bad experience with fish keeping...

So I set up a 29 gallon that I had in my garage and rehomed the fish. Not my method of choice but really my only choice. I took some of the filter media from my planted 55 gallon that is well established and happy and put that into the 29 gallon filter. I have been checking the water twice a day and so far no big spikes in ammonia or nitrite.

I have been doing water changes as soon as the ammonia reaches 0.5 ppm.

Everything was doing fine for a week except the tetra was hiding all the time and there was left over food on the bottom. So I went to Petco yesterday and picked up 4 black skirt tetras and 4 emerald cory cats.

This morning the water was 0.25 ammonia, 0 nitite, 0 nitrate.

Everyone ate and acted normal, except two of the cory cats were dead and their tails were gone... So I took them back to the pet store and got two more this afternoon.

I just checked on them and another one is dead! Looks completely normal though (thinking the shrimp may have eaten the tails off of the other ones after they died).

This is the first aquarium I have ever set up that I used aquarium sand in. I am wondering if it could possible be something in the sand since it only appears to be effecting the cat fish?

Any suggestions? At this point I am thinking about taking the sand out tomorrow and replacing it with some gravel I have...

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[venymae]

If it's aquarium sand I don't see why that would be the reason. I would delve into this more before switching out the substrate.

 

[FishEggs]

Check the ph and hardness of the water too.

 

[JCarnes]

My pH is 7.6 the same as my other tanks. I dont have a test for the hardness, I will pick one up tomorrow.

 

[sheilashoelady]

My corys have only survived in a well established and cycled tank. If your tank isn't heavily planted, there should be a nitrate reading since you used seeded media. How long ago did you set this tank up?

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[severum mama]

It could just be a bad batch. This happens occasionally at every store.

 

[Coursair]

Stop buying fish until you see what the issue is. Also Corys sometimes poison themselves in the bag.
From the net:

"The Poison of the Corydoras

Many species of Corydoras have a poisonous self-defence mechanism against being eaten by much larger fish. All Corys have very sharp fin spines and some seem to give off a low level toxic chemical into the water when frightened or highly stressed.[2] This toxin is believed to be only mildly irritating to people and only if the person is stressing and handling the Cory with their bare hands and is stung.[3] [4]
Self-Poisoning
A rare but recorded event is that at least some some species of Corys appear to be capable of releasing a poisonous mucus from its gills when alarmed which causes itself and other fish in confined volumes of water to rapidly die. Species believed to show this trait are C. adolfoi, C. arcuatus, C. melini, C. metae, C. panda, C. robineae', C. rabauti, C. atropersonatus, C. sterbai and C. trilineatus. This ability is poorly researched and other Corydoras species may be affected. [5][6]"

But I suspect the tank is out of balance or the Corys may be dying of other causes. Poor fishies.

 

[JCarnes]

Thanks for the article, I have never heard of that. I think it may have been a bad batch of fish bevause I have not had any additional issues with them. I currentlt have two that are doing well. I will be adding more later on once the tank is done cycling,