3 of 4 new Cories died

[AshleyD]

Hello
I just bought 4 Corydoras from Petco 3 days ago and three have already died and I am stumped as to why. Here are my water parameters:
Ammonia: 0
Nitrites: 0
Nitrates: 5-10
pH: 7.0
Water temp: 79F
I have a 37 gallon tank with 8 skirt tetras, 4 harlequin rasboras and a snail. Running a Fluval 207 canister filter with 2 sponge filters as well.

One of the Cory’s looked like it had red gills and sores. One negative I can think of is my substrate. I have Fluval Stratum substrate which seems way too rough for them. Any advice or suggestions? I am not sure what to do with the living one as I feel awful that it’s alone now but don’t want to add more if they’re going to die.

 

[Andy Sager]

Hello
I just bought 4 Corydoras from Petco 3 days ago and three have already died and I am stumped as to why. Here are my water parameters:
Ammonia: 0
Nitrites: 0
Nitrates: 5-10
pH: 7.0
Water temp: 79F
I have a 37 gallon tank with 8 skirt tetras, 4 harlequin rasboras and a snail. Running a Fluval 207 canister filter with 2 sponge filters as well.

One of the Cory’s looked like it had red gills and sores. One negative I can think of is my substrate. I have Fluval Stratum substrate which seems way too rough for them. Any advice or suggestions? I am not sure what to do with the living one as I feel awful that it’s alone now but don’t want to add more if they’re going to die.

What kind of cories were they? Some species are more fragile than others.
Because of the time frame, it sounds like they were sick when you got them. I'm pretty sure the substrate was not the cause but let's eliminate some other possibilities: How were the fish acclimated to the tank?
How long were they in the bag from the store?
What if anything did you do with the tank since adding these fish?
Did you see the fish feed since you got them? If yes, what did they eat?
Do you have any pictures of the dead fish?

 

[AshleyD]

Here are the pics I received from my Mom and husband. Unfortunately I was at work so I didn’t get to see them myself but my husband saw some sores on one of the fish today. I also uploaded what the species were. Petco didn’t have a school of the same type but the guy told me they should cohabitate ok with different species.

To acclimate them, I floated their bag and set up a drip to the bag for about 40 minutes. They were only in the bag for about an hour which includes the travel back to my house. I did a 30% water change but no other changes to the tank.

 

[AshleyD]

Forgot to add, I fed them sinking shrimp pellets which I did see them eat.

 

[Andy Sager]

Forgot to add, I fed them sinking shrimp pellets which I did see them eat.

Has anything else eaten these pellets?
Also, were the fish packed together in one bag?

 

[Colin_T]

Did you do the water change before or after adding the fish?

When they were catching the fish at the shop, did they catch them quickly or did they chase the fish around for a few minutes before getting them?

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The gravel is rough but won't kill fish like that. It would possibly scratch their bellies, barbels and face and that could lead to bacterial or fungal infections. However, I would not add anymore bottom dwelling fishes to a tank that has rough gravel. Sand or smooth gravel is much better for them. Sand in particular is what that naturally live around in the wild.

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You should contact the store and inform them of the fish dying. Ask them what the pH, GH and KH of their aquarium water is. Then compare it to your water. If there is a major difference between the shop and your water, it might have contributed to the deaths.

You shouldn't do water changes on tanks that have just had new fish added to them. The stress of being caught, bagged, moved to a new tank, put in potentially different water, and then getting a water change, can be too much for some fish. If you need to do a water on the tank, do it the day before you get the new fish.

You should find out when the shop does their water changes and when they get fish in. If the shop did a water change the day you got the fish, that could be a contributing factor as well. You want to avoid buying fish on the day they do water changes or for a couple of days after they have done the water change.

You also want to find out when the fish came into the shop. If the fish had only been in the shop tanks for a few days they would have been stressed from being shipped to the shop. Ideally you want to get fish after they have been in the shop tank for a week or more, and just before they get a water change, or several days after they have had a water change. This gives the fish more time to recover from being shipped and having water changed at the shop.

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The red patches on the fish look like wounds, possibly from rubbing on something sharp but it could also be from a bacterial infection. Corydoras sometimes stab each other with their pectoral (side) fins when in the bag. This can cause localised infections where they have been spiked. It's not normally an issue if they are spiked from the same species but can be, and it's more likely to be an issue if spiked by another species. It's not common but it might have happened.

The second picture has a fish that appears to be covered in excess mucous (creamy white film over its head and body). This is usually caused by something in the water irritating the fish. It could also be a blurry picture causing the cream appearance.

The third picture the fish looks very pale and almost white. This fish doesn't look well.

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Without seeing the fish when they were in the shop and when you first got them, and without more information about the shop tanks/ water chemistry and how they were caught, it could be a number of contributing factors.

The fish might have had health issues before you got them.
They might have spiked each other in the bag.
They might have been under stress if newly imported or they just had a water change before you got them.
The water change you did might have stressed them.
They might have been stressed if chased around the shop tank before being bagged.

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I would monitor the remaining fish and see how it goes. If it dies, do a 75% water change and gravel clean the substrate every day for a week. this will dilute any disease organisms that might be in the water and reduce the chance of the remaining fish being infected by something.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Don't add any new fish for at least one month. This will give the tank time to settle down and for any diseases to appear, if they are going to.

 

[AshleyD]

The Tetras have definitely attempted to eat the pellets

 

[Andy Sager]

To add to Colin's observations, I don't subscribe to the idea that cories will school/shoal with just any other Cory cat. It doesn't work as often as it does. You are always better off getting a school of the same species when it comes to Cories. If a group of the same specie is not available, I'd wait until it is.

The wounded fish really looks like it was stabbed by another, most likely in the bag, because the timeframe is too short for a massive bacterial infection while the redness surrounding the wound is typical of a cory sting.

The Julii looks almost normal so I would attribute it's demise to stress.

The other fish pictured is too close to see what else could be on the fish as well as if the haze over it covered the whole body.

Pay close attention now to your Tetras to see if they have any reaction to the shrimp pellets. I once lost a whole tank of plecos to some bad algae pellets

In the future, you are better off acclimating in a container if you are doing a drip so get yourself a bucket that will be used solely for fish related things.

As mentioned, you don't want to buy Cory cats that are new arrivals or have recently had a water change where they could be under stress. As hardy as most of the species are, they stress fairly easily.

For now, as Colin mentioned, I would not add any new fish to the tank until you see how the other fish react to this occurrence. When you are ready, and the last cory survived, get more of that specie to form a group of 5 to 6 fish. Keep in mind that Cory cats like water flow as well so make sure you have some form of water current in the tank. If you go to Youtube and search for "Cory cats in the wild" and you'll see they are water that is often fast flowing.

Lastly, I really recommend the use of a quarantine tank for any new fish. Bottom fish can easily carry internal parasites and worms that will not always be visible externally or be active until the fish is stressed. Once you know for sure that your new fish are clean and healthy, they can be added to main aquarium.

Hope this helps.

 

[m.j.gomez]

Here are the pics I received from my Mom and husband. Unfortunately I was at work so I didn’t get to see them myself but my husband saw some sores on one of the fish today. I also uploaded what the species were. Petco didn’t have a school of the same type but the guy told me they should cohabitate ok with different species.



To acclimate them, I floated their bag and set up a drip to the bag for about 40 minutes. They were only in the bag for about an hour which includes the travel back to my house. I did a 30% water change but no other changes to the tank.

Hello, the rule I follow for adding new fish to an established tank is 1in of fish for every 10 gallons of water. This gives your beneficial bacteria a chance to catch up. If to many fish added at once then you can get an ammonia spike or a mini cycle. This link is a good read for adding new fish. Hope this helps!!!!! Ps. Please think about adding a quarantine tank.
https://www.firsttankguide.net/buying-fish.php

 

[AshleyD]

Thank you all for the suggestions, I really appreciate it as I feel awful that these guys didn't make it. I definitely should've waited to do a water change for a few days, but I recently had a brown diatom outbreak and have been diligent about weekly water changes.

When the worker at Petco was netting the fish, he did have to chase them around as they were in a community tank and hard to catch. I'm going to go there today and talk to them and see what their water parameters are and let them know what happened.

Is there any way to add a smoother stone or sand to my existing tank to help the surviving Cory? He's been hanging out on top of the sponge filter. IF this guy manages to survive, I will look into getting more of the same species in a few weeks and using a container to drip acclimate. I do also have a little 10 gallon tank I am not using but can set up as a quarantine tank. And lastly (I think) there is decent water movement at the bottom of the tank with my Fluval Spray bar kit.

 

[m.j.gomez]

Thank you all for the suggestions, I really appreciate it as I feel awful that these guys didn't make it. I definitely should've waited to do a water change for a few days, but I recently had a brown diatom outbreak and have been diligent about weekly water changes.

When the worker at Petco was netting the fish, he did have to chase them around as they were in a community tank and hard to catch. I'm going to go there today and talk to them and see what their water parameters are and let them know what happened.

Is there any way to add a smoother stone or sand to my existing tank to help the surviving Cory? He's been hanging out on top of the sponge filter. IF this guy manages to survive, I will look into getting more of the same species in a few weeks and using a container to drip acclimate. I do also have a little 10 gallon tank I am not using but can set up as a quarantine tank. And lastly (I think) there is decent water movement at the bottom of the tank with my Fluval Spray bar kit.

Most of us have made same or worse mistakes!!!!!. If you still have the fish I believe Petco has a return policy of 30days. Call to make sure.

 

[Andy Sager]

When the worker at Petco was netting the fish, he did have to chase them around as they were in a community tank and hard to catch. I'm going to go there today and talk to them and see what their water parameters are and let them know what happened.

Is there any way to add a smoother stone or sand to my existing tank to help the surviving Cory? He's been hanging out on top of the sponge filter. IF this guy manages to survive, I will look into getting more of the same species in a few weeks and using a container to drip acclimate. I do also have a little 10 gallon tank I am not using but can set up as a quarantine tank. And lastly (I think) there is decent water movement at the bottom of the tank with my Fluval Spray bar kit.

There's your clue that this is not the best person to be catching your fish (imo). Fish shouldn't be chased as much as they should be guided into the net. And with Catfish, they should be using a special close knit netting to prevent the cats from getting stuck in the net.

As for adding another substrate, it really shouldn't be necessary. I did some quick research of the product and it is one of the more recommended substrates for Cories ( as well as other things). I'd leave it be. In the future, if you do another tank, you might want to stick with sand or smooth rounded stone as these are the #1 &#2 recommended substrates. Yours is #3 or #4 depending on which site you look at. As for the water flow, make sure you have areas on the bottom where the flow is blocked so the fish has the option of being in the current or in the still water. You'll probably find your cats playing in the flow then go behind the blocker. That's a natural behavior.

 

[Colin_T]

If you want a different substrate, get some play sand from a hardware store and remove the current gravel and replace it with the play sand. You can also make a sandpit for the Cories. Use a shallow plastic container and half fill it with sand. Put the container in the tank and move some of the gravel away so the container can sit in the gravel. Don't have the gravel more than about half way up the outside of the container or it could mix with the sand.