+1, Mine are typically good after a couple of hours. I normally take mine out when I get home from work and soak in vinegar for an hour or so, then scrub with a toothbrush, quick rinse and put back in. you're return pump, or other filtration would provide enough flow in the meantime. Overnight should be fine if desired, but I typically avoid making any changes overnight like the plague due to past experiences waking up in the middle of the night to see issues in the tank, and getting no sleep while the wife is angry at me for making so much noise at night working on the tank.