In the Balboa swim spa tub system, the number after F (such as F8, F6, etc.) indicates the number of hours of the filtration cycle. Common filtration settings include: ● F2: 2 hours of filtration per day ● F4: 4 hours of filtration per day ● F6: 6 hours of filtration per day ● F8: 8 hours of filtration per day ● FC: Continuous filtration