detritus in a reef tank is normal, as is hair algae in normal reef conditions, the trick is to keep it under control. You make no mention of a
refugium so it's possible that the lack of
macro algaes to compete is most of your problem. Best bet is to start the control cycle. I've rubberbanded a hose to a nylon bristle brush and when I notice algaes (briopsis, hair algae, etc) growing out of control during my next water change I start a siphon and brush the area as clean as possible. This has been working excellently for me as it gets it all out of the tank and most times the algae doesnt come back in those areas.
I run a very high nutrient system so keeping algaes in check is much more of a battle for me than most, so bear in mind my methods may be a little extreme. most people can fight off hair algae by keeping phos and
nitrates in check and simply picking out the existing algae with tweezers or fingers!
