There are soooo many factors that contribute to coral coloration. It does seem that your nutrients are in the high range, but that may be fine in another system. Each reef is different in so many ways and the combination of factors that contribute to how and why a coral may color up or not are just as vast as the system possibilities out there. I have one slimer that started out all red, then went to red with green, and now is turning mostly purple and green with some red left over. Things haven't changed much as far as parameters go but something is happening to cause this change that I am unaware of. On that same note, I have another frag from the same mother colony in a different part of the tank that is pink with green and getting purple tips now. The only thing that is different is where it is placed in my system. Approximately 6 inches higher and at the complete opposite side of the tank. Go figure. Light and flow are the two differences in that piece. What lighting do you have? I have found that as I increase the PAR/PUR and flow and to some extent the color of the lighting this seems to have the biggest impact on coloration. If you can, increase the lighting and flow, slowly, and see if this makes an impact.
