I did a little experiment to see how long I could leave the pool and go on vacation if I brought it to SLAM level before I left. The goal here was to learn the rate the pool dissipated the chlorine so that I would know when I would need someone to come over and add chlorine. With CYA=70, my target FC=10 and the minimum would be FC=5 for my pool. My SLAM level is FC=28. SLAM level is advertised as the level to keep your pool FC if you want to rid your pool of a Algae problem without hurting your equipment by having your FC too high. So I knew this level for the FC would be safe. So I started the experiment...
Day 1 - Raise pool to 28ppm, SLAM level. 5 Gallons of Chlorine.
Day 2 - Loss of 7ppm. Basically 25% of the Chlorine. Current reading 21ppm
Day 3 - Loss of 5ppm. Basically 24% of the Chlorine. Current reading 16ppm
Day 4 - Loss of 3ppm. Basically 20% of the Chlorine. Current reading 13ppm
Day 5 - Loss of 3ppm. Basically 24% of the Chlorine. Current reading 10ppm, my target FC.
Day 6 - Loss of 3ppm. Basically 30% of the Chlorine. Current reading 7ppm. Need chlorine after this to keep pool from reaching 5ppm.
Of course there are a thousand variables (e.g., sun, temp, rain, time of year, etc.) that I am not accounting for, but it appears that the pool loses around 25% of its chlorine until it reaches its target FC which it then loses at a constant 3ppm. On Day 6, I could have someone come over and add half a gallon of Bleach to give me one more day or 5 gallons to give me another 6 days.
I hope this experiment helps others to test their pools to learn how your pool acts so that you can have a trouble free Vacation as well as a TFP.