Steel City Bettas

Weird topic title, I know, but I was wondering if there was any good or bad surface to coat the bottoms of our betta tanks with. I have been using larger typical aquarium rocks of all colors. I know a lot of people use those ellipsed shiny glass stones.

Hmm I have 4 with gravel, 1 with round marbles, and 1 with the ellipsed stones.  That leaves... 7? bare bottomed tanks

I always wanted to try sand.  Sand tanks look so nice.

I think as long as it isn't going to leech chemicals into your aquarium or isn't sharp, and your betta doesn't want to eat it then it is fine as a substrate. 

Oh and it should be noted that all rocks and shells must pass the vinegar test.  Pour vinegar onto the rock in question, if it bubbles, then the rock will ruin your pH.

sand is made of win.

...i dont use anything with the bettas. They are on white bookshelves.