I don't have to really close my pool; temps here don't always get below freezing in the night, and never during the day, and when they do get below freezing I just run the pump. So I kept my pool full in order to be able to run the pump, and kept a solar cover on it to keep the worst of the dirt out of it. So far no algae. I have not added any chemicals whatsoever since November. When it gets warm enough for swimming, should I just do the balance and shock, vacuum, and if necessary get rid of algae, and then swim; or should I have chlorine in the pool for several days before swimming?