Well thanks. I actually ordered some Loudwolf sodium nitrate to dose and see if I can bring it back up to around 10 ppm. We shall see. I never connected the dots with it being low let alone pay attention until you both started talking about it. So maybe that is why I'm seeing it. In any case learned something new and I'll go from there.
Tank and corals don't seem to mind although I still can't figure out why the blue / purple cespitularia melted in less than 24 hours yet my other xenia is doing too well The joys of reefing I guess.
I've been using KNO3 supplements from Green Leaf aquariums for several years and had good results. Might look into them as well if Loudwolf doesnt have what you need.