A waterproof Chlorine Sensor Does anyone know where I can find a Chlorine Sensor to use with the Arduino? It would need to be water proof. I've googled, but I couldn't find anything.

EDIT
Requirements: relatively inexpensive (under $100us), works with Arduino, waterproof and used to detect chlorine in water.
Your best bet would probably be to interface with a colorimeter.  There is a tutorial for an open source colorimeter here:

http://www.appropedia.org/Open-source_colorimeter

IORodeo also sells a shield:

http://www.iorodeo.com/colorimeter

Vernier sells a colorimeter that may be suitable for your project &amp; Sparkfun sells a shield to interface with Vernier sensors.  

If a colorimeter doesn't work you would have to use an electrode, which is pretty expensive and has a shelf life.