just my opinion, but....
the light he's got is tight for that cube. 400watts of actinic pcs would probobly be allright on that cube (jk, but still that tank is only 18").
high nutrients will brown them out to0 right? i know when i mesh modded my octopus and the skimmer bubbled over everything got a little browner in my 46 including my birdsnest... everything tested fine just like normal but everything still turned brown. after that first few days the octo figured itself out started skimming again and it took another 3 or 4 for everything to lose that brown tinge. i've got a e.r on that thing too and it was skimming just as normal during the brown period.
that and i thought i remember something about a seaclone somewhere.