Don’t worry too much about exposing corals to the air when performing water changes. Many corals can sit out of water for 10-15 minutes without killing them or causing any negative effects. However, this only holds true if you turn the lights off prior to the water change, as the corals will quickly burn and dry out if the lights are left on. Keeping this in mind, it’s still a good idea to perform a water change as quickly as possible. The longer you expose the corals, the more potential there is for something to go wrong.