After seeing this kind of rock around town at various stores, I did some research and found an insane deal on 40lb quantities, so I thought I would pass along:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=24528
As long as you buy the 40lb box, it ships free, so its $1.73/lb, half of what local stores sell it for. My box came with a mixture of all sizes, but everything was super porous and very interesting in terms of shapes. I have a bunch of this from a previous buy in my 300 and it livened up nicely.
Enjoy!
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=24528
As long as you buy the 40lb box, it ships free, so its $1.73/lb, half of what local stores sell it for. My box came with a mixture of all sizes, but everything was super porous and very interesting in terms of shapes. I have a bunch of this from a previous buy in my 300 and it livened up nicely.
Enjoy!