I've kicked off 2013 with adding biopellets to my system. They do work!!!
The bacteria that colonizes on these pellets are AEROBIC!!! So they consume NO3 + O2.
Therefore, oxygen saturation level will drop drastically, suffocating other animals. That is main issue with the Biopellets. (Just like dosing Vodka or Vinegar).
Proper setup method would be:
1. closed loop system that feeds low volume
or
2. full blast, but only few (I mean 1/10th of recommended amount) bio pellets in action.
or
3. somehow supply the demand of Oxygen
For me, I added an air tubing from outdoor to my skimmer, (1/2" ID, ~6' in length) and
a Fan that circulates air on top of my sump.