GET A SKIMMER. this will be the first step on the way to removing the
nuisance algae. I have had a similar problem myself and was given the same
advice as you. now I tried this and unfortunately at the same time switched
off the MH and left only the tubes on. virtually overnight the brown algae
turned green and nearly all disappeared. I have only bioballs in the last
chamber (they're next for the chop) but I will remove these at the next
waterchange. the bubble corals have grown considerably and the other corals
seem to have improved too, all stretching to catch light and not being
swamped by it.
just try it and see.
always make notes of any changes and when to see if it makes a difference.

Robin