The difference between ORP and Chlorine/ppm

This outlines the difference between ORP, measured by PoolSense, and Chlorine/ppm (parts per million) that most pool tests measure. It will give you an understanding about the difference and show you how to get the best out of your PoolSense device.

poolsense_2 poolsensor types

Two types of sensors control and disinfect swimming pools.

ORP Sensors

ORP Sensors use electrochemistry and don’t just measure the chlorine but measure the actual electron activity involved in the disinfection process. This means that ORP measures the effectiveness of the chlorine that has been added.

PPM Sensors

PPM Sensors measure free chlorine and measure the free chlorine (both HOCL and OCL-) available to perform the disinfection.

Comparing ORP and PPM

ORP is a measure of how strong the disinfection is at any one time in your pool, but it doesn’t tell you how much disinfectant there is. PPM tells you how much disinfectant there is but not how effective that chlorine might be in killing the bugs.

In the USA and other parts of the world, ORP is widely used to do pool control whereas ppm is used in places like Europe. Whilst there are many factors that govern the relationship, pH and temperature being the large ones. The graph is an indication of the relationship.

Why PoolSense uses ORP

Given that a large portion of the world accepts ORP as a measurement in the control of swimming pool chemistry. And the ORP sensor costs about 20% of the cost of the ppm sensor. ProAutomation has achieved the right balance for our device without compromising the effectiveness.

poolsense orp vs free clorine

The ORP measurement to ensure that your free chlorine can do it’s work is >650mV at the ideal pH of 7.2. You can see from the above graph that this translates to levels of between 1 and 3 ppm of Chlorine. These being the acceptable levels of Chlorine (ppm) in order to kill bacteria but not start affecting the quality of the swimming experience.


PoolSchool ORP vs PPM

PoolSchool – Pool Chemistry

PoolSchool Effects of Low pH