The ankh is an ancient Egyptian symbol. It looks rather like a key. The ankh symbol was used in hieroglyphics and in designs. One of the artifacts carefully placed in King Tut's tomb was an ankh. The ankh must have meant something important to the ancient Egyptians, but we're not sure quite what that was.
You may want to look at my article HERE on lowering stabilizer. Basically if you use chlorine tablets, they have stabilizer in them and over time, can over stabilize the pool water and will need to be diluted. Also calcium levels that are high, rainfall can be a benefit to diluting the water as well.
Most chlorine that you find in tablet, stick or granular form, have cyanuric acid as an ingredient, which is why you only need to add it at the beginning of the year. Nava Chemicals 652025214 Stabilizer and Conditioner, 8-Pound Pail. Add this to your pool at least once and at the beginning of the year.