You could add a tank under neath and have a tube and power head to pump the water out back into the sump.
Slap a light on there, add some organic matter( a handful of soil is fine that's been soaked or boiled for awhile) and DBS, I like grey Coast calicite, but you might find cheaper Arag around also.
The DBS and the macros should remove the NO3 relatively fast once they get going. But you need to realize the NO3 will be driven down but should not be eliminated, macros, and many algae need some low levels of NO3, PO4 etc.
But if you prune the macros consistently and feed the maint ank consistently also, you should be able to balance the system effectively without too much problem.
Skimmers will remove a fair amount of waste but many go either a nice skimmer or a refuge.
Regards,
Tom Barr
