weird monti cap problem

[91YOTA]

as you can see in the pics below, im having a problem with one of my monti caps... sorry for the blurry pics... all other monti's in the tank are fine, all are growing as was this one until this happened... i have 2 frags of this cap from the same location, introduced at the same time... they are supposed to be green but just havent colored up for me for some reason... they are about 8-10" from the bottom in a 24" tall tank with 250w hqi 14k phoenix lighting... any thoughts as to why one "layer" would bleach while the other layer didnt and no other corals are affected? also, it took about 5 days to loose the whole layer....

heres a shot showing placement in the tank... note the other piece to the right of the ricordias...

 

[ronj]

i would guess monti eating nudi's... the time frame sounds about right.. check them out with a flashlight a while after the lights go out.. they are tiny tiny white nudi's that hang out underneath alot