Did the other fish have white
spots all so.
When a fish has whitespot it's best to treat another week once spots have gone.
Cloudy patches can be bad water quality, ph shock, bacterial, parasites, fungal.
Seems strange none of the others have any spots after all this time. One of the head and tail light tetras had what looked like a couple of raised scales. He had a grey coating in places which has dissapeared now, although the original Neon with the white spot still has patches on her. My stats are now Broad PH 7.6 Ammonia 0.25 Nitrite 0.50 Nitrate 10 temp 26 did a 10 litre water change yesterday and a 20 litre the day before.