I have a Salifert Nitrate test kit, and it looks like you are between 50-100, closer to the 100 side. Your comment on Purigen is confusing. It is an adsorption media, and while it can remove organics, it would only be part of the picture to reduce nitrates. You need to remove/regenerate Purigen to burn off the organics, or they will decompose like any other organics if you just leave them in the water long term. Remember, any mechanical filtration needs to be removed and cleaned to actually pull the organics from the system. Not sure if Purigen qualifies as mechanical or chemical filtration.
For long term nitrate control I'd suggest several things in addition to your vodka dosing:
-increased water changes
-limit feedings
-skim wetter
-filter socks for water entering your sump that you clean regularly.
-regularly remove and replace (or regenerate for Purigen) any GAC or similar filter media
I have a 300 gallon net system and I also use a Midwest Aquatic Sulfur Denitrator, which may or may not be something you want to mess with. It is not an inexpensive option.
My nitrates are 0, and I do all the things I suggested above.
Dave