Lowering Nitrates can be accomplished by Vodka dosing or Nitrate destroyer. Both require a skimmer.
Vodka dosing has methanol which binds with the nitrate creating longer protien strings. these cause bigger bubbles in the skimmer, making a better skimmate.
Nitrate destroyer is a simple nitrate eating bacteria. Added daily, they consume nitrate, creating nitrogen gas and then quickly die. Corals will eat the bacteria, but a skimmer will remove them as well.
Having no corals, I'd go with vodka dosing as it is easy and cheaper. Google the technique as there are a few experienced people out there with detailed instructions.
I used both techiques to lower my nitrates in my FOWLR
system (had climbed to about 80ppm) once I got a skimmer.