Yeah, if your running a HOB filter, you have to make sure that the intake isn't close to the substrate or you could end up with a ruined impeller. That said, I've had no problems with the AC150 on my 20 long, which uses a sand substrate. All the plants in it are doing really well, too. I've used sand, flourite, and ecocomplete. Sand's fine if that's the look you want. You just have to take a little care with it.