Is this fertiliser burn?

[OrchidLoverSA]

Hello all, this started out as a couple of small white spots on the new growth. At first I thought it was scale, but on closer inspection I couldn't find any critters. Still, I wiped the whole thing down with surgical spirits. Now the white spots have turned into a white blotch (see pictures). The only change in culture has been weekly fertiliser instead of every second week. Could that be it? Some of my other orchids also have small white spots on the new growths.

http://www.orchidboard.com/community...py-phrag-2.jpg

Oh, and it's culture is as follows: Hot, humid, bright light, standing in a tray of tap water (tap water is very orchid friendly in these parts).