Pygmy corydoras dying again

[Beastije]

Hi guys

I am so confused. I bought another batch of pygmy corydoras, after not having much luck with them the last time. I quarantined for two weeks, zero issues, moved them to the tank they will be staying at. There were four other pygmy corydoras from previous purchase (purchased a batch of 10 in October 2023, lost most of them, purchased a batch of 10 different seller August 2024, lost most of them)

A week after a move, two of the pygmies are dead.

Tank is 60x30x30 cm so 54 liters. Temp is 24°C, ammonia zero, NO2 zero, pH 7,5

I am wondering what the hell. I thought in my previous attempts it was feeding, as I always fed little and occasionally, so this time I feed daily, sometimes even twice a day. Dry food with insect content, hatched BBS, microworms, frozen cyclops.

It is not even the same tank as the previous attempts, though ofcourse my water is the same and the sand I use could be the same. I have sand most of the space, some pebbles, leaves, alder cones, plants, slow gentle filtration, access to surface, air pocket with a lid to prevent cold air water breathing.

I am at a loss

Perhaps it is the pH? This batch for sure was wild caught. Spent three weeks with the seller who must have had similar water to me, or around 7, then two weeks in the quarantine now week at a tank. I thought my ph was a bit lower, other tanks show 7, thought the cones would bump it down a bit.


What now? I have more alder cones that I poured boiling water over, so I could add just the cones or the with water. I did a water change yesterday when I first found the body, found another body, might do another 10 liters. I drip the water in to avoid shock.
The only thing I notice before they die is they are paler.

I wonder what I could try. Thanks

 

[GaryE]

I would do nothing. 20% losses soon after arrival are pretty normal, especially from online buys that had the extra stress of shipping. If the losses continue on, then there's a worry, but 8 out 10 surviving isn't bad. It should be, but it isn't.
I can't remember - do you have a good water movement in the tank?

 

[Beastije]

But it has been three weeks since I have had them, just a week in this tank. The water doesn't move much, a bubbler and some flow but not a lot

 

[GaryE]

I consider the first 6 weeks to be quarantine, though 8 weeks might be more sensible of me.

When I've had pygmy Corys, they've liked moving water.

 

[Beastije]

Ok I can try increasing the water movement, I have a regulated air filter since I have them with least rasboras
I bought 16 this time to have a nice big group so they would be comfortable

 

[Colin_T]

What do the fish look like when they are sick or dead?
Do you have any pictures of the sick, dead and living cories?

What is the nitrate and GH of your water (in numbers)?

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If the fish were fine in the quarantine tank and the pH is 7.5, it should be ok for them, although it's a little high for wild caught fish, but that won't be the problem.

If they were fine in the quarantine tank but started dying in the display tank, then it's something in the display tank.

Where are you getting the alder cones and leaves for the tank?

Have you gravel cleaned the sand recently?
If not that's a good place to start, especially when bottom dwelling fish start dying.

When was the last time you cleaned the filter?
If it hasn't been done in the last 2 weeks, do it now.