Chlorine 101

Testing your water regularly is extremely important – to keep it properly sanitized, safe and in balance.   In this article, we’ll address just chlorine – the different types, their effectiveness and how to test for them.

The chlorine in your water is in two forms – free chlorine and combined chlorine.  Free chlorine, the good chlorine, is what kills bacteria and viruses and oxidizes contaminants.  When you add chlorine to your water, you’re actually adding free chlorine.  When free chlorine combines with contaminants such as bacteria, body oils, suntan lotion, etc., it becomes combined chlorine also known as chloramines.   Combined chlorine has very little sanitizing or oxidizing ability.

Total chlorine is the sum of both the combined chlorine and free chlorine in the water.  Free chlorine is the total amount of chlorine available to be used as a sanitizing or oxidizing agent.  Ideally, you do not want combined chlorine.  So, in a perfectly clean pool, the total chlorine level  would be the same as the free level.  But, as a pool accumulates contaminants, combine chlorine forms such that the amount of total chlorine will be higher than the free chlorine.  Shocking  or superoxidizing the pool will help eliminate any contaminants, breakdown the combined chlorine, and get the total and free chlorine levels back in balance.

Testing for chlorine

There are generally three methods for testing chlorine: a handheld meter, drops or test strips.  Any method is acceptable.  But… take care to note what type of chlorine you are measuring.  Some methods measure free chlorine, some measure total chlorine and some measure both.  For example, a kit that uses red “DPD” drops will measure free chlorine whereas kits that use yellow “OTO” drops measure total chlorine.

Remember, total chlorine is simply the sum of both combined chlorine and free chlorine.  The combined chlorine value should never exceed 50% of the free chlorine value and should be as close to zero as possible.

Finally, to ensure a well sanitized pool you should maintain the free chlorine level in the range of 1-3ppm (2-4 ppm for spas).