They way I used it (like 6 x last year
) was...shut off skimmer; treatment 1; wait 48 hours; treatment 2; wait another 48 hours; 20% water change; fire skimmer back up. So 96 hours, not 72. Be careful though. Even with the 20% water change, the skimmer will want to play funky for awhile.
As for the airstones...I tried that the first time, but what a hassle. Saltcreep everywhere. If you have good flow, your water will be oxygenated enough without them.
HTH and good luck,