First and foremost, keep your parameter in check with water changes, if needed. Then in the mean time, a new soft toothbrush will work for cleaning off the rocks, coral, snails, and crabs. Run any filters you have and clean as needed. Your tank will get messy/cloudy. That should clear up in a few hours. I would not recommend turning off the lights with corals, maybe reduce the time that's it. What algea did you inherite? That may clear up with a good cleaning and your parameters being better. HTH