Thanks Colossus!
The black substrate is Black Diamond sandblasting sand. I got it from a place that rents and sells sandblasting equipment. I love the sandblasting sand, except that the colour washes out the bichirs. The Black Diamond is similar in texture, but the colour works great with the bichirs.
I just set up a new tank using straight Black Diamond. I'll try and get some pics up.
Thanks Kevin! The female is very round. I can't believe how much she eats compared to the male.