Try diluting your pool water with distilled water. First try 1:1, then try 1:2, 1:3, until you get a reading on your OTO cell. If it's 1:1, double the reading. 1:2, triple it. 1:3, quadruple it (so if it reads "5" it's really 20ppm). That will give us a ball park on the true total chlorine level.