Like many in this forum I switched to aquarium sand from aquarium pebbles and like it's appearance and ease of cleaning. I used black sand in my big tank and light/nearly white in several others. The fish in the lighter sand tanks seem more skittish. When I have moved them to black sand substrates they seem MUCH happier. I am referring to several kinds of tetras and swordtails.
Anybody notice this kind of response in your fish?