Green Monti. Dig. question for sps gurus

[Dez]

First off, here are the specs of my tank

46 gallon display tank lit with 2 x 400 watt radiums and a 55 watt actinic pc

75 gallon sump in basement filled with 50 or so gallons (some live rock in there)
54 gallon in basement hooked to same sump with one clown and an anemone
40 gallon frag tank hooked to same sump in basement with 250 watt 10K halides

Calcium reactor
Kalk reactor
Huge beckett skimmer

Last I checked -

Calcium 440
Alk - 4 meq/l
Sal - 1.024 (I think)

I haven't measured Nitrates etc...

Anyway.. All of my sps are growing very well... I have 6 different caps all growing

Acros seem to be growing
Birdsnest frag is at a standstill..

I have brown monti dig and brown with purple tipped monti dig that are growing..

However, every single time I try a green monti dig frag...it seems to brown out...then slowly die. I don't get it.

I gave a frag a couple of years ago to Canadian Man and his colony is huge. I got a frag back from him after my 150 tank crash and I can't keep them alive. I've gotten the green one from someone else and same thing...slowly browns, then dies...

The other monti digs are doing well in my tank, orange from Delphinus, browns, and the purples... It's very frustrating because I think green is my favourit colour of the digitatas...

Argh

Any ideas?

Des

Oh btw, I've tried the frags in my frag tank with 250 watt lighting and also under my pc's and in my display tank... I don't get it.