something attacking my green polyps?

[claytontong]

the gsp has been doing well for months and has displayed some slow growth. I noticed some white spots appearing on the stalk of some of the polyps recently - they don't seem natural to me. do I have some kind of disease breaking out? please see the picture.
water - ammonia, nitrite, nitrate = 0
ph = 8.3, salt = 1.026
in the picture, the problem stalks are in the middle. to the right, you can see some healthy ones. note that the reddish hue is due to the picture - there is no color differentiation up and down the stalk; the actual color is close to what is show towards the top of the stalk.

 

[aquarius77]

What are your other water parameters. What kind of lighting and how old are the bulbs? I have never seen anything like that before?
The thing that strikes me odd is that they are still open.

 

[claytontong]

alk ~ 2.3, ca 400 ppm
2 x 175W MH 10k, 2 x 56W PC 10k, 2 x 56W PC actinic
polyps are directly under one of the MH, about 1 foot deep. MH bulbs are new, 2 of the PC are newer, 2 should be replaced anytime (12+ months on them).
at first I thought the spots was just tiny sand grains sticking to them, but they definitely seemed attached. they appear to stick out slightly, like a sand grain sticking to it, as opposed to a spot that's just a discoloration on the surface.

 

[aquarius77]

I dont know what to tell you? Your alk is low and maybe give it less light.