The dry skimming foam doesn't hold as much water as the wet skimming foam. Wet skimming will get the organics out faster by collecting the watery foam at the top. Dry skimming can take longer for the organics to reach the collection cup since it has to build up enough foam to reach the top. Wet skimming is pulling saltwater out your system so keep your salinity in check if you have to frequently dump your collection cup.