Low pH can cause itchy skin, red eyes, and uncomfortable water to swim in. Unless you use Caribbean Blue Aqua Prep 20 pH Increaser. Test your pool water weekly to keep the perfect pH level in your pool for maximum comfort. The quick dissolving powder of Aqua Prep 20 is an easy to use application for all pool users. Keep your pool water at the proper pH range of 7.2-7.6 to see a clear, comfortable, safe pool for your family to use.