I was doing a WC on my 10 gallon this evening and left the HOB filter running while I siphoned 25% of the water out. With the water level down, the HOB was like a waterfall pouring into the tank, agitating the surface, creating bubbles, and putting off a pleasant sound. It was also kind of cool to see the surface of the water through the glass, which is typically concealed by the hood. I was thinking, is there any reason not to run the tank like this all the time? Other than having enough water volume for the inhabitants, I can't think of any other reason why this would be detrimental.