iF YOU ARE IN THE PORTLAND AREA YOU CAN GET ACTIVATED PREMIUM COCONUT SHELL CARBON FROM SEAHORSE AQUARIUM SUPPLI IN BULK FORM. iT IS THE GOOD STUFF. Anyplace that sells live corals will also have it.

15 Pounds - 5 Gallons Bulk Lignite Aquarium Carbon - English

I agree...its probably cheaper to buy one premade.