A good way to find out about sweepers is to check the tank after the lights are out for a few hours, a few days in a row. I have had torch corals that didn't sweep for 3 or four days and then BAM, it was sweeping 6 inches all arround it one night.
VERY IMPORTANT - if you change your powerhead/current arrangement in your tank, think about how this changed water flow is going to affect your coral's sweeper action. I have made this mistake before, and got a leather that was safe before all stung to heck.