One of the main things that most chain stores don't tell you is that they are actually a brackish water species. When we had ours, they were in a 10g. I used river bed gravel. They love to pick through it. You can get a little creative with their tank. Put some small plastic plants in there and they'll climb through them. Pretty neat.

I also used a standard HOB for the filter. What I did was to create a waterfall effect with rocks. Worked well. Take some bigger rocks like slate to provide them some cover.