I keep reading that some fish (like kuhli loaches and panda corys) do better with sand substrates instead of gravel, since they can be injured by the sharp gravel. I've never actually seen an aquarium set up with sand instead of gravel, though. I'm wondering, how would you go about keeping a sand substrate clean? I use a normal syphon-type cleaning tube on my gravel . . . but if I used this on sand, wouldn't it just suck the sand right through the tube? Not to mention stirring up a lot of sand into the water?