Three of the four lowest adsorbing carbons were pellet shaped. The pellets had smooth, hard surfaces. The most effective carbons tended to be irregular in shape and offer a large surface area to volume. The surfaces of the more effective carbons were rough rather than smooth like the pellet carbons. While there are many brands of carbons sold to hobbyists, there are a limited number of types of carbon sold.
Bituminous coal based carbons make up the majority of brands available.
Lignite based carbons make up the rest with the exception of a few coconut based brands. This may have affected the outcome of the tests. For example, only one coconut carbon was tested, and it was a mid-pack performer. This suggests that had I been able to acquire more formulations of coconut, coconut based carbons may have performed better. One wonders what marketing forces would have prevailed if Spotte's findings had been as widely read as Hovanec's.