What makes stony corals go brown in color?

[nasotang00]

I guess the subject says it all. What makes stonys like acro go brown. I have a few blue tips and other supposedly bright colored acros, but they won't show their true color? I have a 55g with dual 175w blueline mh's, 1 96w 8k pc, 1 96w blue actinic pc and a 65w blue pc. Lights are approx 7 inches above water line. Water params are:
sal: 1.026
Ph: 8.4
cal: 450
alk: 3
phos: undetec
ates: 10 - 20 ish
ites: 0
amon: 0
Does too much light cause this or not enough> What could be the prob?
Thanks all

 

[josh]

Your alk is a little low. Too little lights makes the coral go brown and too much bleaches it. Move the coral to the top of the rocks.
HTH

 

[nasotang00]

All stonys are at the top of the tank and have always been. All about 3-5 inches from water line. Have had no bleaching problems.

 

[bang guy]

Ca and ALK balanced, Phosphate down, and food. What are they eating?

 

[josh]

I totally missed the most obvious question. How long have you had this little guy? Was he brown at the store? It will take a few weeks to start to color up and adjust to the new lights.
HTH - a bit more
~ one other thing, how old are the MH lamps? When the lamps start to loose their power ( lumens/lux etc ) the corals will start to brown up.