I'm changing my gravel substrate over to sand. I tried using a funnel, but the sand still ended up floating at the top, no better than before. My water also went cloudy, but that should go away in time. I scoop out the gravel with a net, then put it in a container to dump out later. I'm doing this in increments because I don't want to disturb BB too much. I rinsed my sand in my water change container, so I can't change any water out until I'm done adding sand. I might have to buy more sand because the current layer isn't thick enough to root my plants like the gravel did.