Perfect Range: NONE

A healthy pool should have NO Combined Chlorine! Combined Chlorine is "used up" Chlorine that has "Combined" with swimmer waste and other debris.

Combined Chlorine is Chlorine which no longer has any sanitizing capability.
Combined Chlorine gives off a strong offensive Chlorine smell even though Total Chlorine levels are relatively low. This usually indicates that the pool needs to be super chlorinated with large quantities of Free Chlorine.

If there is no strong Chlorine smell and the water has a crystal clear appearance, you can probably just add enough additional Chlorine to achieve "Breakpoint Chlorination" or "super chlorination".

Breakpoint Chlorination requires that you add enough additional Chlorine to equal 10 times the amount of Combined Chlorine.

Example: If Combined Chlorine is 0.5 PPM you would add 5 PPM of Free Chlorine.

If the water is not otherwise in perfect shape you should Chlorine "Shock" the pool by raising the Free Chlorine level of the pool to 10 PPM.