Death of my Black Neon Tetras...

Yesterday morning, I spotted white spots on my black neon tetras. Fearing that this may be fungal infection, I transferred them to another smaller tank.

The next morning, I managed to obtain a fish medicine (a form of antibiotics known as Tetracycline) from my friend. Upon returning home in the evening, I spotted one of the black neons to be swimming upside down. This was a bad sign. Nevertheless, I added the medication and hoped for the best

1 hr later, I found both black neons to be lying at the bottom of the tank, upside down and motionless

I then found out that these white spots are caused due to cold temperatures. Experiencing cold weather these past few days, this might have been the cause. However, this can be minimized by adding salt during change of tank water.