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I have a 50G tank with about 30 assorted tets - rummynose, candy cane, pristellas, and blood fins.
I have 6 pepper cats (corydoras paleatus), 3 small albino corys, 3 kuhli loaches and a 2 small plecos.
They have all been together for many months - the paleatus have been in that tank a year. All of a sudden my paleatus are hanging at the surface. All my water parameters check out fine. Temp is constant 80F always. I am very vigilant with water changes, etc.
Any thoughts on the sudden change? It is ONLY the paleatus that have changed their activity. I don't know if they're looking for food or looking for air. The filter is working fine, surface area breakup and flow haven't changed.
Any ideas?

Hi,

You got a mystery there. I have had one cory "Hugging the Surface". I was a panda and sadly it died 2 days later. But all member of the species in a tank no. I hope you your don't end the same as mine.

Hi all,

Popeye wrote: ↑25 Mar 2020, 21:49 I have 6 pepper cats (corydoras paleatus), 3 small albino corys, 3 kuhli loaches and a 2 small plecos.
They have all been together for many months - the paleatus have been in that tank a year. All of a sudden my paleatus are hanging at the surface. All my water parameters check out fine. Temp is constant 80F always. I am very vigilant with water changes, etc.
Any thoughts on the sudden change? It is ONLY the paleatus that have changed their activity. I don't know if they're looking for food or looking for air. The filter is working fine, surface area breakup and flow haven't changed.
Any ideas?

It is likely to be an oxygen issue.

Could you add an air stone? and reduce the water temperature? and is it a planted tank?

cheers Darrel

Thanks guys -
I'll try lowering the temp a little and move my water flow intake up to get more surface area exposed for oxygen exchange. I think I'll also move the 3 larger Roseline Sharks to a different tank - very active and use a lot of O2. Every little bit may help.
Thanks again.

Sorry Darrel, missed your last question - yes, it is a planted tank - swords and java ferns.

The C paleatus are the only fish in your tank preferring cold water, and colder water can contain more oxygen than warmerwater. Further, a fish in warm water will need more oxygen than in cold water.

That is, your C paleatus could very well be the most sensitive to low oxygen levels - even though Corydoras are able to breath atmosferic oxygen through their guts.

80 F, that is 27 C, is further a bit high for them

I’m no expert but I’d add an air stone if I had a pump and see if it helps.