My daughter's betta "Coquin" died. I wonder why. We bought him in a local pet shop 2 months ago and installed it alone in a cycled 25 liters (6.6 US gallons) heated to 25°C (77°F), covered and filtered (200 l/h, with a baffle placed to break the current). I changed approx 10% of the water each week.
He was feed thanks to small "Ocean nutrition" pellets and JBL NovoBetta. He was in good shape, always checking whatever was in front of the glass, eating well. No visible problem whatsoever.
Then I searched a new home for a female corydoras aeneus albinos, living in another aquarium since mid-2012 (she's probably blind), checked on the Web that they can live together, and installed her with him.
I saw some (rare) somewhat decolorated scales on Coquin, but I cannot remember if it was before or after the cory's installation in his aquarium.
There was no apparent problem.
Five days later Coquin was in a state of apathy, didn't eat anymore and had a white patch on the side. I medicated (eSHA 2000). In approx 24H he was staying vertically (head up) in a corner (see picture 1).
24H later he died on the bottom (see picture 2)
The cory is perfectly OK (she just layed eggs)
Given the symptoms and cadaver appearance I suppose he had some fungal infection, or body slime infection, or maybe columnaris. Any thoughts?