Sailfin,, this really hurts to hear of your losses. I experienced this during my last rebuild, when I changed over to Zeovit. I am convinced the problem was the release of nutrients from the sand. I should have done this more slowly as to minimize changes in the water. I did not read higher readings in nitrate, rather in PO4, which I believe was bound to the aragonite sand due to using a 2-part calcium method. I have now gone over to using my reaktor again and am much happier. PO4 has gone down and stabilized, but that doesn't bring back the P. xanthometapon, A. leucosternon, various Anthias, etc.
One thing I have learned over the years, an easy/hard lesson, and that is to keep conditions as close to NSW as possible and stable. This precludes any big changes in the tank. As I am maintaining a very low nutrient system, I need to monitor parameters weekly, such as NO3 (1mgl), PO4 (0.01mgl), K+ (390mgl), Ca (430mgl), Mg (1300mgl) and salinity (1.024 @ 26°C/79°F). My prefered levels are in parenthesis. Note that there are some nutrients. A no nutrient level is just as bad, if not worse.
Once a tank is stabile for a few weeks, I maintain minimal dosing of various supplements, plus 5-10% weekly water changes with a balanced salt. Currently, I consider only 2 salts balanced enough; Reefers Best (Korallen Zucht) and Coralife. Both are very close to NSW. These salts minimize the necessity to dose potassium.
I realize you probalby know all of this, but I though I should just reiterate for others and to sort of put it all together.