Cathy,
The Spa will not normally get any fresh water unless the spillover is working. Three hours a day sounds like a lot to me, but it really depends on how much water is moving.
I assume that you are not doing this manually, and that you have an automation system. Assuming that you also have a VS pump, at what speed is the pump running when the spa is in the spillover mode?
I suspect that you could drop back to running the spillover for about 60 minutes a day, 20 minutes at a time... You can adjust the schedule and then start measuring the FC in the Spa and make sure that it stays at about the same FC as the pool water. If the FC in the spa drops below your minimum, than change the schedule to 30 minutes at a time. etc.
Thanks,
Jim R.