Please remember I mention to you that you have to introduce just a little GFO to your tank, until your tank goes to that first phase with little GFO is the time to add little more, do not use all of the GFO that I gave to you once, that much could shock your system, I filled that much just because I tough giving as much as I could to the person who was going to buyed, but it's not for only used once.
I have bought BRS GFO from another member here and I had some bought from Ebay, they're the same granular size, which comes to dust very easy but a wash before use should remove smaller particles and dust, BRS had some bigger grain before wich was able to regenerate if intented but the price for it was almost double, and the regeneration process of the media wasn't guarantee to work.
Hope it helps. Thanks.