I have an in ground pool, which is 16 x 32. It holds 19,000 gallons of water. Every year, I have an issue with reading chlorine. For example, this year, we opened our pool two weeks ago. After opening, I added 12 gallons of liquid shock and the pool is still not reading a chlorine level. After days of letting the chlorinator run on full, it is still not reading any chlorine with the test strip. I ended up draining 18 inches and refilling the pool with fresh water seven times. I just recently added 1 gallon of Muriatic Acid and 5 pounds of powder shock. Hopefully, i am working in the right direction, but are there any tips or ideas on how to keep the chlorine level up at all times?