If I was a betting man, I would bet it was my sustained low alkalinity that probably started the STN. My colonies at the time were really taking off with growth...like a massive growth spurt. I had to adjust my reactor every week or two to keep up with demand. I kept my alk around 9-9.5. By the time I got to tending to the tank my alk was sitting @ around 3. My CO2 tank was empty too. Another possible factor was the sudden spike in alk. I probably bumped it up too fast trying to get it back to my regular levels. I did 10% weekly/bi-weekly water changes. That might also be a small contributing factor?Looks like you had great success with this tank. Neglect will be punished in this hobby, but I am still curious what you did or did not not do in those few months which have led to the crash, if you are willing to share this for lessons learned?