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If you ever anticipate being gone for a longer period of time, buy a chlorine float. Get it ahead of time to allow yourself time to mess with it and get it dialed in. With a float, you can leave it for a month.
I left my tub for 18 days and came home to crystal clear water. I use the Bromine frog and I also lowered my temperature. Oh and I didn't miss my tub at all.. I was in Tuscany lol!