Montipora digitata question

[Delphinus]

I thought this stuff was supposed to be like a weed?

I'm obviously doing something wrong here. I've got a frag going on, what is it, going on three months I think, and it hasn't done a dang thing in my tank. Not a millimetre of growth, no encrusting at the base, not even polyp extension. It just sits there in perfect stasis.

Ca=400ppm, Alk=4.0, NO3=0.0.

My guess is, the difference must be either something about the water current, or the lighting. Mine sits underneath a 250W halide (6500k); should I perhaps move it away from the bulb or even into a bit of a shadier area?

(However .. if it is perhaps the light is too much, wouldn't I see polyp extension at night?)

Hints/tips/advice? (please and thank you)