You could read the articles on this site to gain a better understanding of how a toilet works. You may have a flapper that needs replaced, your water level in the tank could be too high allowing it to run over the overflow tube and/or your refill tube could be inside the overflow tube resulting in siphoning. Remove the lid on the tank and observe it's operation. It may be a value to replace the fill valve with a Fluidmaster 400A and to replace your flapper.

If you pay for your water, you're probably wasting a lot of money.

After you fix the problem (probably the flapper) stop using bleach-based tablets or other products in the tank. They ruin rubber flappers over time.