Yes, use the old water. Add the recommended amount. Open all valves so all jets run. Open all air vents (and if applicable turn on air blower). Run all pumps on high for 20-30 minutes. Wipe off any residue. Add half the amount your originally added then run the jets for another 20-30 minutes. If you get more stuff out you can repeat as needed. Once done drain and refill. Be sure to wipe off any residue as/after it drains, once it starts drying it's hard to get off.The Ahh-Some should arrive either today or tomorrow. So, 1) use the old water that's currently in the tub with the Ahh-Some to clean the system? Then, 2) refill with tap water and adjust chemicals accordingly?