Planted Tank Enthusiast
Join Date: Jul 2012
Location: Northern Colorado
i used a cheap black sand that i found majorly discounted at a lfs, and it still looked pretty natural...at least more than black gravel or eco complete.
if you are capping dirt, I think sand would probably be your best option. anything larger might let some of the mud seep out....and trust me it gets messy quick.
though keep in mind; if you like to shuffle plants around a lot, a sand/dirt substrate may not be your best bet