I know there are some clever work-arounds for this out there already, but Hanna finally made a low-range Nitrate checker:
www.hannainst.com
Looking at the instructions though, it’s kinda more complicated than I thought it would be.

Marine Nitrate Low Range Checker® HC
Accurate. Repeatable. Marine nitrate testing made easy. No more subjectivity! Ideal for aquariums and marine biology applications.

Looking at the instructions though, it’s kinda more complicated than I thought it would be.