When you changed out the aquarium did you clean your sand or get new sand? If you don't mind me asking what are your nitrates now? TBH For a long time I was running nitrates around 80ppm (I dont do water changes). Like you, recently, I upgraded my display, did a 100% water change and used the old water to clean my sand. Started running a refugium and dosed plenty of AquaVitro's Seed and now have been sitting at .10 or lower. Obviously everyone's system is different... Hope everything is going well. Any new pix of the new display? Ever heard of the Reefers Moonshine Theory? Was life changing for me and my tank.... Heres a pic of my new displayYes but it took a rip clean of the tank and replacement with a bigger one!
The tank those readings were in had failing seals on the bowfront. Without a full rip clean they would have never come down though. Sand was loaded with years of gunk and rock pores filled. New tank runs high as well but manageably high and the corals don't mind it go neither do I.