Hi Gary, I suggest purging the tub with the water that is there. Use a good purge like Ahh-some jetted tub cleaner. Once that's done, empty the tub and refill it. When you refill, add a stain and scale remover to the fresh water. Rinse your filter cartridge after 24 hours to release anything that it's collected. You should be using a new filter cartridge.
Good luck,
Sandy
Caledon Hills Pool and Spa Supply