Well, after getting my BRS order in today, I put some GFO in a filter sock and put it in my Biocube. It sits in a shelf mod after running through cheato in the middle chamber. I added about 1/2 cup that gets really good circulation. Well looking today at Aquatek's Tunze GFO label, I read that caution is necessary on the amount of GFO, and that GFO can cause too rapid of a nutrient decrease that potentially could cause coral death. I guess that I am wanting a little peace of mind from someone who has used it.(being my first time). So please let me know how you used it and how it worked for you. And also if there is something that I need to be aware of.