You should consider your sump as a the same tank as your main tank. By turning it off at night you are reducing the water flow in the sump therefor alowing the water to become stagnant, which is not good. It becomes a breading ground for all kinds of nasty little creatures, much like a swamp breads mosquitos. Is this your regular regiment for your set up? If so I could have aided in the outbreak of marine velvet.
