No skimming because it will skim the meds right out of the water. You don't have to worry about your bacteria load taking a hit...but you should worry about properly oxygenating the water when you treat the tank.
I kept my skimmer on to oxygenate the water, removed the cup, and allowed the skimmer to overflow into the sump. If you're dealing with an HOB skimmer, then I suppose that won't work, but basically...if you skim you won't be treating the fish.
Dose right away and toss an HOB on the tank with a couple powerheads pointing toward the surface for oxygenation. If you're worried about waste causing ammonia to spike in the tank, then do small water changes and add back in a small amount of prazipro with the new water.
