user490: 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.

user1184: 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 & 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.

490: <p>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.</p>

<p><strong>EDIT</strong>
Requirements: relatively inexpensive (under $100us), works with Arduino, waterproof and used to detect chlorine in water.</p>
 1184: <p>Your best bet would probably be to interface with a colorimeter.  There is a tutorial for an open source colorimeter here:</p>

<p><a href="http://www.appropedia.org/Open-source_colorimeter" rel="nofollow">http://www.appropedia.org/Open-source_colorimeter</a></p>

<p>IORodeo also sells a shield:</p>

<p><a href="http://www.iorodeo.com/colorimeter" rel="nofollow">http://www.iorodeo.com/colorimeter</a></p>

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

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