I have never had the problem I have now and it is very frustrating.

Every day when I check the chlorine level it is on zero. I keep my automatic feeder full and turned all the way up and I have started placing 3 tablets in the skimmer. (I have a 20,000 gal pool). I have been shocking it about 2-3 times a week in an effort to get the levels up (using about 4 pounds of trichlor). On the evenings I shock, the next am level is still zero. My stabilizer level is normal. This is becoming more expensive as I am running through my shock. What in the world is going on?