I have been using Equine fresh pine pellets. i got the pine pellets because I was breeding rats and couldn't stand the smell. And it worked. Had a whole lot left when I started with ASF's, so I used it.
That said... 2 weeks ago I switched 2 of my ASF tanks to aspen..... HOLY COW.
HANDS DOWN, WITHOUT ANY DOUBT, the aspen tanks after 2 weeks have WAY less odor then the pine pellet tanks that were cleaned on the same day as the aspen tanks....
I can honestly say, for whatever reason, the aspen tanks smell better today, after two weeks of 1.4 and 40+ babies living in the tank, then they did the night I threw fresh aspen in...
Many people claim that ASF's have no natural smell.... others say the stink after a week... well, from what I have seen first hand, the ones that stink after a week are using pine pellets.... the ones that dont' are using aspen.
Someone, Anyone, test this and report back....... It is one of those things that you won't belive unti you smell it...