I think it's 3 or 4 -- it will auto-magically boost you within 4 hours of reaching the threshold. But I just did it manually.

If your pump is ON and water is flowing through the chlorinator, that counts. I don't know your system, so you'll have to make sure that's happening when you vacuum.

However . . . rather than running 1x for 12 hours, it's much better to run 2x for 6 hours, even apart from the vacuuming.