My pool is an in ground concrete with 20,000 gallons built in 1974. I have had no major problems in maintaining chlorine levels till now. In Oct 2013 I drained and re-filled the pool and added the chemicals Leslies supplied me with to balance the water. My current readings are as follows: calcium hardness 250....cyanuric acid alkalinity dissolved solids 100..........I have two floaters in the pool each with 3" trichlor tabs. I started with 2 tabs and am now up to 3 tabs in each floater and yet I get a reading of less than 0.5 fac. I am using an OTO test on my chlorine test. The only time I get a strong reading is when I put in 2lbs of Leslies power powder.............and the pool is not being used! What can be the cause of this?