You need to narrow the possibilities with some research.
1. Does the tank drain completely then slowly fill up before the next cycle? Don't guess or assume. Check the level immediately after the next cycle is complete. 2. When the cycle empties the water, does it come out with force or does the pressure seem low? 3. Is the water softened or is it hard? If you can't really tell, take a sample of tap water to Sears. They will analyze for free.
I had a similar problem several years ago. The problem was a very small scratch on the disc that controlled the water flow for the recharging cycle. It allowed water to leak into the tank.