Why are my SPSs bleaching? Please Help

[wojo]

Hello everyone,
i tried everything so i am turning over to you guys for help. for some reason my montis and blue tip stag are bleaching away. it first started with some of the blue tip frags and then next one, and now the mother colony has at least one tip starting to loose color.
same goes with montis, i have already lost one 3x4 inch piece or a red one, now the green one is starting to slowely bleach out, soft film forms on it and when its gone it pure white.

all of my softies are doing great, also other SPSs are growing and stuff, i really have no idea what to check next.

here are my params, taken today with Salifert test kits:

NO3: 0
Phos: 0
Ca: 420
Kdh: 9.0
Mag: 1290
sg: 1.026
ph: 8.2
Temp: 80-82 F

i feed phyto every couple of days, when i feed my fish i mix frozen mysts & brine, with frozen formula 2 so the whole tank eats.

BTW: i did check for red bugs and was unable to locate any.

any help or suggestions on what to check next is very appreciated.

thanks,
Wojo.