i'm not expert but i had sort of your problem.
i have a 37 gal tank with 175w 15k iwasaki , i do water changes every week and my corals still weren't coloring up (they were horribly brown).
i decided to make a frag rack and start moving up my corals...well so far my rainbow monti is starting to color up and my acro looks way better in color....so in a few may be you should try moving up your corals (may be one of your brown ones and see how it takes it), compare your water params with another friend and see what they get.......just a few ideas
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