Sorry, no idea really. Well some ideas. Just like us, if we get too chilled it can put a strain on the immune system and a bacterial infection or virus can take hold--or one of a few other things.
I think it is the same with our pets.
When the temps fluctuate I get chilled and then I get hot and my body thermostat just can't get the right adjustment. I don't know if it was the albinoism or just the fish, but that guy has taken ill. It wouldn't surprise me if albinos are more suseptible to chill than some other fish. Is the albino the same species as the other?
I lowered the water temp on my small Cories (pandas, arcuatus, melini, San Juans.) At the same time I added some new baby pandas. The lowered temp spurred the San Juans to spawn, but the stress caused a crash when one of the babies died, and then there was a chain of deaths. I lost more fish than I want to count, including the gran dam San Juan lady that left me a nice net of fry.
The Great Panda Plague has run it's course now. And it looks like the tank will stablize.
If you have a quarantine tank, move the sick fellow and treat him nice. Perhaps he will recover. Without more info, it is not possible to suggest a treatment other than simple good care.
