Hi DesertDorkus, You have a great question. You can safely switch to bromine anytime, but once your hot tub is on a bromine sanitizing solution, you can’t switch back to a chlorine sanitizing solution without draining and refilling with fresh water. Even though you can switch over to bromine now, we recommend you take this opportunity to drain your hot tub, refill with fresh water, purge, balance and then add the FROG Serene (bromine) cartridges at that time. If you refill with fresh water, please be sure to follow the setup instructions included in the system kit and add a new Serene Mineral Cartridge (blue cartridge), along with a Jump Start packet to make sure the bromine is activated and your water is ready to go. We hope this helps! If you have any questions, we’d love to answer them, please call us at 800-222-0169 or email us a customer.service@kingtechnology.com We hope you try FROG Serene – we know you’ll love it!