What is Killing my Corys?

[Ken Sauer]

Approximately 2 months ago, I purchased 6 young corys and put them in a 10 gallon quarantine tank. After quarantine, I added them to my 125 gallon community tank. Then, I got 4 more young guys and put them in the 10 gallon. Within a week, one of the 4 got a bladder infection. I took the the other 3 out of the 10 and put them in the 125 and treated the guy with the bladder infection. A day later, I found a cory near-dead on the bottom of the 125. He died. The rest of my corys looked healthy at this time, so I decided to take the dead one and the one with the bladder infection back to the lfs.
A week later, another cory died...found him barely breathing on the bottom of the 125. The next week I found another cory in the same situation. A few days later another died.
In speaking to the lfs, they said that perhaps, the corys, since they are so young are having a hard time getting enough to eat (in the 125 I have 8 zebra danios, 7 cherry barbs, 12 candy canes) with competition for food and all. So, I moved the remaining 5 corys back to the 10 gallon tank. The all seemed healthy at the time. 3 or so days ago, one of them started acting funky and mopey. He eventually died the same way the others died. Now, I am down to 4 corys. Obviously, I am trying hard to keep them alive. They are all in the 10 gallon. The perimeters in both my tanks are perfect and have been the whole time.
I caught the one I took pictures of looking a bit mopey this morning and it made me worry that, in a few days, he will be dead at the bottom of the tank.
So....here are some pictures of the one acting a bit mopey.
Does anyone see anything obviously wrong with this guy?
All suggestions are appreciated.
Thanks.

 

[Fish4dawin]

Approximately 2 months ago, I purchased 6 young corys and put them in a 10 gallon quarantine tank. After quarantine, I added them to my 125 gallon community tank. Then, I got 4 more young guys and put them in the 10 gallon. Within a week, one of the 4 got a bladder infection. I took the the other 3 out of the 10 and put them in the 125 and treated the guy with the bladder infection. A day later, I found a cory near-dead on the bottom of the 125. He died. The rest of my corys looked healthy at this time, so I decided to take the dead one and the one with the bladder infection back to the lfs.
A week later, another cory died...found him barely breathing on the bottom of the 125. The next week I found another cory in the same situation. A few days later another died.
In speaking to the lfs, they said that perhaps, the corys, since they are so young are having a hard time getting enough to eat (in the 125 I have 8 zebra danios, 7 cherry barbs, 12 candy canes) with competition for food and all. So, I moved the remaining 5 corys back to the 10 gallon tank. The all seemed healthy at the time. 3 or so days ago, one of them started acting funky and mopey. He eventually died the same way the others died. Now, I am down to 4 corys. Obviously, I am trying hard to keep them alive. They are all in the 10 gallon. The perimeters in both my tanks are perfect and have been the whole time.
I caught the one I took pictures of looking a bit mopey this morning and it made me worry that, in a few days, he will be dead at the bottom of the tank.
So....here are some pictures of the one acting a bit mopey.
Does anyone see anything obviously wrong with this guy?
All suggestions are appreciated.
Thanks.

In the first picture he looks extremely thin. You might want to try and add some small sinking wafer so that the corys can get some food. This is if they haven't been eating which I don't know. Where did you buy the corys from?

 

[Ken Sauer]

In the first picture he looks extremely thin. You might want to try and add some small sinking wafer so that the corys can get some food. This is if they haven't been eating which I don't know. Where did you buy the corys from?

I bought them from a local fish store. Yeah, I've been doing that. They have been in the 10 gallon about a week now. Since then, one died. I'm hoping it was maybe just a feeding problem that, perhaps, the last one to die just wasn't strong enough to survive. In the 125 gallon tank the other fish would eat the sinking pellets after eating their own food. Thanks!

 

[Fishiemang]

That substrate/gravel may decimate their barbels, making it difficult for them to find food. Sharp rocks tend to cause issues with cories. Not saying this is the case, as one of my tanks has that glofish color crap, but the stuff you have has actual sharp edges that can injure their barbels. In one pic that looks to be what happened to the pepper, but they also lose them for water quality issues or when they are sick.

Since you started having issues when you added the second set, I would suspect that you got a batch that were unknowingly sick, and in haste of transferring the 3 seemingly healthy specimens to the main tank early, it may have spread whatever it is to them.

Just a.couple ideas for ya.

When I first got into corydoras, I musta lost a.dozen or.so before I got some that made it. Not sure what killed them off. Had a panda that lasted a month. Had an albino that lasted 2 months. Had another 10 in a.couple tanks and they made it about 2 months. Said I.would never buy them again because they die, but the old lady talked me into getting a pepper, julie and emerald, so I did. They still here 3 years later so....I chalked it up to I got a bunch of duds.

 

[Ken Sauer]

That substrate/gravel may decimate their barbels, making it difficult for them to find food. Sharp rocks tend to cause issues with cories. Not saying this is the case, as one of my tanks has that glofish color crap, but the stuff you have has actual sharp edges that can injure their barbels. In one pic that looks to be what happened to the pepper, but they also lose them for water quality issues or when they are sick.

Since you started having issues when you added the second set, I would suspect that you got a batch that were unknowingly sick, and in haste of transferring the 3 seemingly healthy specimens to the main tank early, it may have spread whatever it is to them.

Just a.couple ideas for ya.

When I first got into corydoras, I musta lost a.dozen or.so before I got some that made it. Not sure what killed them off. Had a panda that lasted a month. Had an albino that lasted 2 months. Had another 10 in a.couple tanks and they made it about 2 months. Said I.would never buy them again because they die, but the old lady talked me into getting a pepper, julie and emerald, so I did. They still here 3 years later so....I chalked it up to I got a bunch of duds.

Interesting, isn't it? They are the only fish I have lost and yet they are supposedly "very hardy." Thanks for sharing.

 

[Sgooosh]

Interesting, isn't it? They are the only fish I have lost and yet they are supposedly "very hardy." Thanks for sharing.

yes i had one that died because of sharp rocks. you might want to add some sand on top if u are getting more. also try different foods such as algae wafers, fish food, veggies and things so he(?) might eat it

 

[Fish4dawin]

Yes sand is the ideal substrate for corys and loaches so there is no in between sadly. If you have gravel it will most likely destroy the corys barbels. This could be the cause of why they are dying because they depend on their barbels to feed and without them they will become skinny as seen in the picture above.

 

[Fish4dawin]

Also Merry Christmas!

 

[Colin_T]

Trying to sum this up.
You bought some Corydoras and quarantined them for a while. They seemed fine so you put them in your main display tank.

You bought some more Corydoras and put them into quarantine. A week later one of them was sick so you moved the remaining fish into the display tank.

The fish that was left in quarantine died and now the fish in the main display tank are dying.

All the Corydoras have now been moved into the quarantine tank?

The quarantine tank has the broken rocks on the bottom of the tank?

----------------------
How long did you quarantine the original fish for?
Did you quarantine the second batch for one week?

All new fish, plants, snails and shrimp that you want to add to an established aquarium should be quarantined for at least 2 (preferably 4) weeks.

Nothing comes out of the quarantine tank until everyone in it has been healthy and shown no signs of disease for at least 2 (preferably 4) weeks. If a fish gets sick, everyone stays in quarantine and the 2-4 week period starts when it is better.

By moving the 3 fish out of quarantine when one was sick, you introduced whatever the problem is, into the main tank.

----------------------
Can you post some pictures where the fish are in focus?

What is the ammonia, nitrite, nitrate and pH of the tank water?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do water changes?
Do you dechlorinate the new water before you add it to the tank?

What symptoms do the fish have?
Are the fish eating well?
What does the fish's poop look like?

 

[Ken Sauer]

Trying to sum this up.
You bought some Corydoras and quarantined them for a while. They seemed fine so you put them in your main display tank.

You bought some more Corydoras and put them into quarantine. A week later one of them was sick so you moved the remaining fish into the display tank.

The fish that was left in quarantine died and now the fish in the main display tank are dying.

All the Corydoras have now been moved into the quarantine tank?

The quarantine tank has the broken rocks on the bottom of the tank?

----------------------
How long did you quarantine the original fish for?
Did you quarantine the second batch for one week?

All new fish, plants, snails and shrimp that you want to add to an established aquarium should be quarantined for at least 2 (preferably 4) weeks.

Nothing comes out of the quarantine tank until everyone in it has been healthy and shown no signs of disease for at least 2 (preferably 4) weeks. If a fish gets sick, everyone stays in quarantine and the 2-4 week period starts when it is better.

By moving the 3 fish out of quarantine when one was sick, you introduced whatever the problem is, into the main tank.

----------------------
Can you post some pictures where the fish are in focus?

What is the ammonia, nitrite, nitrate and pH of the tank water?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do water changes?
Do you dechlorinate the new water before you add it to the tank?

What symptoms do the fish have?
Are the fish eating well?
What does the fish's poop look like?

The original fish were quarantined for 2 weeks. The second batch of 4 were purchased and put in quarantine after the first batch went to the main tank. A week into quarantine, one fish got a bladder infection. He was in very bad shape and I was afraid he would die. I took the other 3 out and put them in the main tank early. The one with the bladder infection got much better after the pea treatment and quarantine for about 3 days. On the third day, a cory died on the main tank (I don't know if he/she was from the batch of 6 or 4). At this point, I was becoming exhausted from cory problems and thought none of the corys in the main tank looked good, let alone the guy doing better in the quarantine tank. I was in constant communication with the local fish store and I asked if I could just bring back all 10 (including the 1 dead fish for a refund). They agreed. My daughter and I (it's a hobby both of us share) moved out all the rocks and plants in order to do the big catch. When we did so, the corys in the main tank got active and my daughter decided she wanted us to keep the 8 that remained in the main tank (since they suddenly looked healthy) and take back just the dead one and the one with the bladder infection. We did so. I don't know if the guy with the bladder infection lived because the fish store put him in with a bunch of other small corys. Out of that tank at the store they told me (a week later) two had died so they don't know the fate of the one I took back. In any event, a week later another cory dies. The next week 2 corys die within days of each other.
So, I call the fish store and, because all the other fish (other than corys) are fine in the main tank they suggest that I either got a bad batch of corys or because these guys are so young they are having a hard time competing for food with the other 27 fish in the tank. They offer for me to bring them back and switch them out for older, fully grown corys.
I ask my daughter and she wants to keep them.
So, I move the remaining 5 to the quarantine tank. Out of the 5 one begins to act mopey and fatigued. Each day he becomes worse until finally he's not moving at all and dies the same death all the others died. So, after his death I keep a close eye on the remaining 4 to see if any of these are showing signs of being a bit mopey. One is a little mopey. The other 3 are full on energy. So, I send out this original thread. This was 24 hours ago. Today, the mopey one (the darkest one in the pictures) continues to be mopey, fatigued and just kind of sits in the same place. He is definitely less active than he was yesterday. The other 3 are full of life, etc. just as he was at one time. Now, I fear he will die in a couple days and then one of the remaining 3 that look great now will start acting like he is acting now until they all die off.
The ammonia is zero, nitrates are zero, the ph is 7. I clean the gravel every week with the water changes. I dechlorinate water before adding. Yes the sharp stoned tank is the quarantine tank. I changed the filter a couple weeks ago for the first time. Usually, I wash out the filter once a month and put it back.
The 3 active fish are eating well, the less active one is eating some. I have never seen the fish poop. In the pictures, the one who is now acting tired, mopey, not looking great is the dark one (he is in 3 of the pictures below). The others are full of life.
Thanks so much!

 

[Colin_T]

The ammonia is zero, nitrates are zero, the ph is 7. I clean the gravel every week with the water changes. I dechlorinate water before adding. Yes the sharp stoned tank is the quarantine tank. I changed the filter a couple weeks ago for the first time. Usually, I wash out the filter once a month and put it back.

What is the nitrite level in the tank?

How much water do you change when you do the water changes?

How do you go about cleaning the filter?

You mentioned changing the filter a couple of weeks ago, what did you do in regards to that?

What are you feeding them?
How often are you feeding them?

---------------------
FILTER CLEANING
When you clean a filter, you should wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn.

Do not replace media unless it is starting to fall apart. If you have to replace any of the media, only replace one piece at a time and try to keep at least half of the old media in the filter. If you replace all of the filter media, you get rid of the beneficial filter bacteria and can have ammonia or nitrite spikes that can affect the fish.

If you have filter pads/ cartridges in the filter and want to replace them, get some sponge for another brand of filter and put the sponge in where the filter pad would normally go. Sponges will last for years and don't need replacing on any regular basis.

You can use a pair of scissors to cut sponges to fit so if in doubt, buy a bigger sponge and cut it down to size.

I don't know if you have any carbon or zeolite in the filter but you don't need carbon (small black granules) or Ammogon/ Zeolite (white granules) in a filter unless there is a water quality problem. Even then the best thing to do if there's a water quality issues, is a big water change.

---------------------
FEEDING
Feed the fish 3-5 times per day for a month, with a variety of dry and frozen (but defrosted) foods. Make sure you do lots of big water changes and gravel cleans when feeding more often, to keep the tank clean.

Most pet shops sell frozen bloodworms, brineshrimp, daphnia and marine mix. You keep these foods in the freezer and take out one block and feed it to the fish. These are all good foods to use to fatten fish up and the extra food might help the fish fight off the problem.

Wash your hands with warm soapy water after handling frozen fish food because it can carry bacteria, and some people have allergies to the bloodworms. Most people don't have any problems but be careful when you first use them, just in case.

---------------------
SUBSTRATE FOR CORIES
I would remove the substrate that is in the tank and replace it with something smooth and fine. Sand would be ideal, or a smooth round gravel. The course substrate will make it more difficult to feed and will also damage their barbles.

---------------------
In the mean time, wipe the inside of the glass down with a clean fish sponge.

Do a 75% water change and gravel clean the substrate every day for a week or until we work out what is going on. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Increase surface turbulence/ aeration to increase the dissolved oxygen in the water.

Add some salt, (see directions below).

---------------------
SALT
You can add rock salt (often sold as aquarium salt), sea salt or swimming pool salt to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (1-2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

When you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

 

[Ken Sauer]

What is the nitrite level in the tank?

How much water do you change when you do the water changes?

How do you go about cleaning the filter?

You mentioned changing the filter a couple of weeks ago, what did you do in regards to that?

What are you feeding them?
How often are you feeding them?

---------------------
FILTER CLEANING
When you clean a filter, you should wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn.

Do not replace media unless it is starting to fall apart. If you have to replace any of the media, only replace one piece at a time and try to keep at least half of the old media in the filter. If you replace all of the filter media, you get rid of the beneficial filter bacteria and can have ammonia or nitrite spikes that can affect the fish.

If you have filter pads/ cartridges in the filter and want to replace them, get some sponge for another brand of filter and put the sponge in where the filter pad would normally go. Sponges will last for years and don't need replacing on any regular basis.

You can use a pair of scissors to cut sponges to fit so if in doubt, buy a bigger sponge and cut it down to size.

I don't know if you have any carbon or zeolite in the filter but you don't need carbon (small black granules) or Ammogon/ Zeolite (white granules) in a filter unless there is a water quality problem. Even then the best thing to do if there's a water quality issues, is a big water change.

---------------------
FEEDING
Feed the fish 3-5 times per day for a month, with a variety of dry and frozen (but defrosted) foods. Make sure you do lots of big water changes and gravel cleans when feeding more often, to keep the tank clean.

Most pet shops sell frozen bloodworms, brineshrimp, daphnia and marine mix. You keep these foods in the freezer and take out one block and feed it to the fish. These are all good foods to use to fatten fish up and the extra food might help the fish fight off the problem.

Wash your hands with warm soapy water after handling frozen fish food because it can carry bacteria, and some people have allergies to the bloodworms. Most people don't have any problems but be careful when you first use them, just in case.

---------------------
SUBSTRATE FOR CORIES
I would remove the substrate that is in the tank and replace it with something smooth and fine. Sand would be ideal, or a smooth round gravel. The course substrate will make it more difficult to feed and will also damage their barbles.

---------------------
In the mean time, wipe the inside of the glass down with a clean fish sponge.

Do a 75% water change and gravel clean the substrate every day for a week or until we work out what is going on. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Increase surface turbulence/ aeration to increase the dissolved oxygen in the water.

Add some salt, (see directions below).

---------------------
SALT
You can add rock salt (often sold as aquarium salt), sea salt or swimming pool salt to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (1-2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

When you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

Thanks so much!!! What a great help. ( :