How can I measure the chlorine content?

To determine the residual Halamid® concentration in water one can do Halamid ion testing in which you measure the chlorine content:

Chlorine can be easily measured using strips, like you can find here.

This gives you a rough indication if chlorine is still present at ppm level.

You could also use a titration test like:

• https://www.merckmillipore.com/INTL/en/product/Chlorine-Test,MDA_CHEM-114801

This gives you an exact figure.

There are also electronic devices available in the market:

• http://www.youtube.com/watch?v=cSlR8VnVkDs for a simple tester from Hanna.
• http://www.testequipmentdepot.com/extech/pdf/cl200.pdf which presents a 1 step process.