My skimmers producing a lot more than without carbon dosing , lighting is maxspect r6 160w
Yea a skimmer should produce more waste with carbon dosing.. It is removing bacteria from the water column that is feeding on Nitrates, phosphates and carbon.
While I am not real familiar with Maxspect lights and settings but they are a decent brand of lighting. With led's it depends on what it is set at and what the par is at the coral. Leds have really made lighting more complicated. You look to have the coral mounted higher up so it could be adjusting to the different light. It is not bleaching so it probably is not too much light.
Darkening brown color usually means not enough light. Zooxanthellae are brown and produce food for the coral. A coral will increase zooxanthellae in low light conditions to produce more food for the coral. So the idea is to bring down the amount of zooxanthellae so the other colors show through. That said I would not just go and increase lighting just yet because it may just be acclimating and it could be caused by higher nutrients or even the lighting from the LFS at this point. It takes a while sometimes.
Sometimes it is just time. About a year ago I purchased this bright purple acro and placed it in my lagoon. It went light tan in color after a few weeks. After about 6 months it started to color back up. Came back as bright blue and not purple though. My lights were different, my parameters are different so it was just changing.
Personally I would start with what Griss said and bring down PO4 and NO3 and start there and see what happens. It looks like you have some algae so your nutrient are probably higher than you think too. It looks like you are addressing this issue already so you seem to be on the right track.
What ever you decide do it slowly.
It looks healthy so you should be fine.
