For many in the northern United States, Memorial Day marks the ceremonial opening of the swimming pool. That means it’s time to start the yearly rites of summer: adding skimming, filtering, testing and adding chlorine. Oh, yeah, and swimming, diving and relaxing, too! These days, there are high-tech answers to every pool problem, from cleaning, to water treatment, from lighting, to pool safety to how to listen to your favorite tunes when you’re relaxing on your brand new raft. Here, then, are five great gadgets you need to have the perfect pool experience this summer.