As some of ya'll know I am reading and learning all I can from other forum members tank builds until I learn enough to sit up my own large tank up grade. I have always thought that if you were going to have a tank that it was a given, you had to have a sand bottom as opposed to a bare bottom or it just wouldn't look good. I am starting to change my mind a bit on this issue, maybe. I still don't like the idea of just a glass bottom in a tank but I read something the other day in a build and I am not sure what this is. This person was buidling a tank with a PVC bottom in their tank, what is this.