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I would consider a bromine floater at that point. Keep it set low, use a bubble blanket and remove your pillows before leaving. Set the temp at 80 or lower.
In your case with the time periods you are away I would go with my plan B and that is to convert the tub to a salt generator chlorine system using a “saltron mini” https://www.youtube.com/watch?v=Zq6Of9aeudII have a friend that has this system and it works very well. There are a few other similar devices that work the same way the saltron one seemed to be the most common.