Typically during the winter months, homeowners do not have to worry about their pools quite as much. With the cold temperatures and lack of sunlight, algae tends not to grow. With this in mind, a lot of pool-people tend to wait until late into the spring to open their pool. This may save you a few bucks, but it also gives those pesky spores time to grow. With a solid safety cover its usually fine to wait, but if you have a mesh cover or poly cover, there are a few minor steps you can take to ensure your pool is nice & pristine upon opening. Every few weeks pull up a corner of your cover. Depending on your pool's size, put in a few pounds of shock. Next, take your brush & brush the chlorine out toward the center of the pool. Doing so will circulate the water and spread the chlorine throughout the pool. Every time you do this, do it on the opposite corner.