I had bought my set up used and the previous owner had black gravel with some larger, smooth dark blue gravel in there. I wasn't crazy about it but it was OK. After a couple weeks of indecision whether to put Black Diamond, just plain old sand, or leave it alone, I upped my school of Cory Cats and realized I should just do it. I went with pool filter sand thinking that I could always add the black later if I wanted to darken it up some. I spend a good part of my Saturday morning washing sand, got the old stuff out (I used a new, rinsed, dust pan) and added the sand. I can't tell you how happy I am that I did this! The tank looks larger and my Tiger Barbs look great against the light bottom. My Cories seem much happier too! I have never seen them out and about as much as I have in the last 24 hours. Of course, the down side is that I can easily see the... ehem... "dirt" everyone is leaving but I'll have to get over that for at least a week at a time - until vac/water change day. lol There is no question here. Just pointing out that even though it took up a good part of my day, it was so very worth it!