Thanks to the advice on this site we went on vacation for 12 days and came home to a almost algae free pool. I brought the FC to 18, covered it,turned the pump off. When I returned home I still had a FC level of 4. I had no algae except one small spot that I found in the skimmer. I brushed it away when I turned the pump on. So do you think I would need to shock or just wait and see what happens?