Thanks both. Ben, no I'm not running GFO at the moment, but one of my next jobs will be putting in an order with Premium Aquatics, including for a couple of reactors, one to run GFO and one to run GAC. People seem to have success with Algaefix as well, so I'll get some and try dosing that. I was planning to put in an order for my next bulbs anyway, so I'll just expand the order. I might hold off on the Rabbitfish if I can, as I know that it'll end up being too big for the tank, so I'd end up just giving it back to the shop after 6 months (shops here never give credit for returned livestock, they just happily take back for free and then sell on

). The downside is that I'll have to remove the drop-in fuge in order to fit both reactors in my sump (there's no room outside the sump either). But I'm not convinced it's doing much anyway, so no big loss really.
Budha, thanks for the Naso recommendation. I'd seen the same thing, but what goes for the Rabbitfish in my 65g goes double for a Naso tang I suspect!