One type of leak occurs when the toilet is overfilling in the tank. This type of leak is easy to recognize and no tools are required: just lift the tank lid off the tank and look to the "overfill tube" generally located in the center of the tank. If the water level in the tank is to the top off this 1" diameter tube, the toilet is overfilling and is most likely to be constantly running water through the toilet and down the drain! This repair generally means replacing the fill valve assembly to ensure a complete repair.
The other type of leak occurs when the flapper or flush valve seal has deteriorated or otherwise become ineffective. This type of leak can be identified by performing a simple dye test. All you need to do is discolor the water in the tank with food coloring or other non-toxic dye, leave the toilet unused for 10-15 minutes then look in the toilet bowl. If the water in the bowl has become discolored this means the flush valve seal is leaking. Repairing this could mean replacement of the flush valve assemble depending on the actual cause of failure.
If either of these are occurring it is costing you money and wasting a lot of fresh water; and you may not know it is occurring because both types of leaks can be silent.
The Dual Flush Pro kit is the perfect solution to prevent or correct both of these leaks at a cost that pays for itself in just a couple month on average and the best part is you get the option of choosing a half flush vs a full volume flush every time you use the toilet. You can lower your water bill and help save water.