Thought I'd report back, it's been a while. The refugium didn't really go as planned, I've since removed it all. I added a Red Sea Reefmat 1200 Rollermat, and added the 3rd Ecotech light. The Reefmat is amazing, very satisfying hearing it rotate once it's filled :D
I had a bit of a green hair algae problem, so added a Kole Tang, and I also added a Christmas Wrasse (hides pretty much the whole time!). A sand-sifting starfish has also helped.
Realised my RO/DI needed replacement too, which may be the cause of the algae.
Just BAU mode at the moment, maintaining Alkalinity at 8.4 and Calcium at 420.