Panda Corydora Sensitivity to pH

[benmeier]

I have a 10 gallon tank that is cycled and has a couple of plants. I had three panda corydoras (starting to stock the tank, with the goal of 6 fish). Everything had been stable with weekly 25% water changes; the water parameters have remained 0/0/0. My region has hard water, and the pH has been stable at 8.4 (the corys had been acclimated to these conditions from the LFS). After the last water change, two of the corys developed pop-eye and quickly died.

In my effort to try to figure out what was happening, I tested the water parameters again, and discovered that the pH had dropped to 7.8. I have not added anything to the tank other than clean water and food, and I use a dedicated bucket for water changes. I tested the water from my tap and discovered that the pH is significantly lower (7.2) than it typically had been in the past - so I think that some change in my water supply is responsible for the change in pH.

Is the change in pH the cause of the pop-eye and loss of my fish, or should I be looking for another cause? The remaining cory is lonely, and I would like to get some new companions, but I don't want to cause the death of any more fish.

 

[Colin_T]

pH fluctuations don't cause cloudy eyes or popeye. It is caused by poor water quality and bacterial infections. Because the tank is new and your water quality is good, then I doubt it is a water quality issue.

How long did you have the fish for before they developed popeye?
If you only had them for a few days they might have had a bacterial infection when you got them, or they were injured when being caught, or they injured themselves in your tank, possibly on the gravel.

Check you gravel for sharpness. Take a few granules and hold them with your fingers on one hand, then rub them across your other hand. If they feel sharp or scratch you, then it is too sharp for the Cories. If it does scratch you then wash the scratched skin well with warm soapy water so you don't get an infection.

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pH fluctuates depending on water supply. In Perth WA, the water corporation adds more ground water in summer because the dams have less water and this drops the pH. In winter the pH goes up.

 

[benmeier]

Thank you Colin_T. I have had the corys for 3 weeks before the pop-eye appeared.

The substrate is fairly fine. I did the test as you suggested; I don't think its too sharp, but I might not have the right calibration. I would compare it to table salt or granulated sugar in both size and texture. I have watched all the corys sift through it happily.

I forgot to mention that when I did get these fish, there was also a dwarf gourami that died three days later. I had attributed that to the stress of the new tank.

I’m suspicious of the pH change simply because this began within 24 hours of a water change, although I do realize that it could just be a coincidence. I'll have to look into my utilities to see if the source could have changed.

 

[Colin_T]

If you are using sand it should be fine for the Cories.

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Having the fish for 3 weeks before the issue developed means the problem came from your tank. If the water corp changed the water supply or added extra chlorine/ chloramine after doing work on the pipes, that might have contributed.

The final factor is the dwarf gourami. They are renown for having health issues and carrying diseases like TB and the Iridovirus. TB takes a long time to kill a fish so that is unlikely. The Iridovirus weakens the fish and causes sores and the fish dies from secondary infections.

The dwarf gourami might have had a bacterial or protozoan infection and that has now spread to the Corydoras.
Can you post a picture or short video of the remaining fish?
And check them to see if they are rubbing or scratching on any objects in the tank.

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When you do water changes, do you dechlorinate the water before adding it to the tank?
If no then you should start doing that. Get a bucket of tap water, add dechlorinator and aerate for about 30 minutes, then add the water to the tank. This allows the dechlorinator to come in contact with all the chlorine/ chloramine molecules in the water and neutralise them. It also allows the dissolved gasses in the water to stabilise after being under pressure in the water pipes.

 

[benmeier]

Yes, I dechlorinate with Prime at least 15 minutes in a deadicated bucket before I add it to the tank. I also agitate it some too. Perhaps I should wait a bit longer; I’ve been contemplating preparing the water a day ahead.

The remaining corydora remains normal in appearance and behavior, with the exception that since it is alone, it hides most of the time and only make appearances when fed. Current photo is included.

The first cory that died appeared bloated; I did not examine the second one that carefully. Both became less active towards the end. I have not seen any of the fish rub on any objects.

One other thing that I have noticed is that a piece of drift wood that I got at the LFS at the same time as the fish has developed something fuzzy on its surface. I’ve also included a picture of that.

 

[Colin_T]

The fluffy stuff on the driftwood is fungus. It happens a lot with new wood that is put in water. It's fine and will go in a few weeks.

The remaining Cory looks ok apart from a mark just in front of the dorsal fin but that doesn't appear to be anything major. So probably just monitor the fish and if no more issues during the next 2-4 weeks, then add some more. But if there are any issues during that time don't add anything. And if you have a quarantine tank then put the new fish in that for a month before adding to the tank.

 

[benmeier]

Thank you Colin_T for the advice. I will carry on with observations of the remaining corydora for a few weeks.