Long overdue update, last 6 months tank has preformed how I hoped. Parameters are stable; corals and fish doing well. I stopped using vinegar dosing several months ago and NO3 went lower??? I believe it was due to po4 limiting? Parameters have been stable for months: no3 @ .05; po4 @ <.015; alk, cal, etc good. I have reduced water changes to about 10 gallons a day and once a month detritus removal and with the Sulfur Denitrator working well, nutrients are no longer an issue. Still using GAC, and GFO is not needed. IMO, po4 was being stripped too aggressively, causing corals to slowly starve, and denitrifying bacteria to limit no3 uptake. Interesting that since stopping vinegar and no3 going lower, I have more algae growth on the glass and in the fug; and a few spots of cyano. Pics coming soon!