When I first installed my Penguin BIO-Wheel 350, I had extremely fine sand as a substrate. Less than an hour later, the filter was making loud grinding noises. At first I thought it was defective, but after exchanging it, the noise came back. I tried cleaning the filter thoroughly multiple times , but the sand would get right back in. I tried using socks and all kinds of sponges over the intake. Nothing worked. I finally gave up and took the sand out of the tank. I'd love to put the sand back in since my crayfish loves to dig in it. I should mention that, even though the intake was several inches above the substrate, my crayfish kicked it up a lot. Would I be better off getting a different type of sand? I would hate to have to go through this again.