Zero Nitrates?

I have a 110Gal FOWLR tank that is over 3 years old.. Mostly small fish but one Dog Faced Puffer who is a messy eater. I have always had problems with nitrates. When I got the tank it was already over 2 years old and running with nitrates at 160.
The nitrates were high for along time, aggressive water changes would bring them down some (never below 80) but they would climb back up, mostly due to over feeding. I was new and wanted to keep everyone happy. Now feeding is much more conservative.
Last month I converted part of my sump into a refugium and added a couple of different macros and a cleanup crew to the main tank. Chaeto is the most prominent, I have a piece that is about the size of two fists. Slowly my nitrates have been coming down, for a week they were between 5 and 10, its hard to tell sometimes with the API kit. This morning they were at zero, I checked it again and sure enough zero. Ammonia and nitrites are both zero.

My questions are..

It this possible to have zero nitrates with a medium loaded tank?
Is this OK, the macros have to have something to eat and grow? Or is it that they are just doing a bang up job and have enough to consume?
My red nuance algae continues grow next to the refugium light but not in the DT. I think part of it is that I switched to LEDs on the tank...
I want to add a yellow tang and a few more small fish to add color to the tank and get rid of the algae that is still there.

Ideas?
Thanks in advance!

 

Congratulations on getting the NO3 down, the macro's are doing exactly what you bought them for...if you were to be monitoring PO4, you would have seen it come down as well.

We have our 120 with a very heavy load, it is doing well with the refugium. My NO3 will creep up to 20 every other month or so...and a couple of water changes will get it back down... I suspect as soon as the macro algae takes over the refugium, the NO3 creep will stop...