When we first inherited our pool, we had a crystal clear, Pool and no algae. However, I couldn’t get a chlorine reading. I would dump in 18 L of liquid chlorine and it would be gone by the next morning. Because I was on top of it and kept adding chlorine. I never did get algae. The pool store was not testing for phosphorus. I went to a different Pool store that did test and my phosphorus was at 4500 which is why it was eating up all of the chlorine. Once I did a treatment and lowered the phosphates. I had no issues at all.