Fish tank monitoring

It might be interesting to monitor chris's fish tank electronically.  I am thinking we need some sensors and then an interface box and finally some way to display the dat on the internet.


http://www.ebay.com.au/itm/pH-C-ORP-EC-CF-TDS-Monitor-Meter-Tester-LED-19990-PPM-/330569569690?pt=LH_DefaultDomain_0&hash=item4cf77b559a

What parameters to monitor?
How do we monitor chlorine?
pH
Temp
TDS = Total Dissolved Solids
EF
CF

ORP (Oxidation-Reduction Potential)

Item number:330548031460
$89..90
This Newest multi-function water quality tester is the succeeding version of PHT-026. This pH monitor can simultaneously measure water quality with seven different parameters including pH, °C, °F, Humidity (%R.H.), EC, CF and TDS without changing electrode. This is a user friendly water quality monitor which can be used in Aquarium, Pool and Hydroponic purposes etc. Compared with PHT-026, this pH monitor is featured with a Large, Quad View LCD Display. The monitor also has stand on the back with light weight design. The pH electrode has BNC design so that it is replaceabl

Item number:330569569690
$95.30
This Newest All-in-One multi-function water quality tester (PHT-028) is the succeeding version of PHT-026. PHT-028 can simultaneously measure water quality with six different parameters including pH, °C, ORP (mV), EC, CF and TDS. PHT-028 is a user friendly monitor which can be used in Aquarium, Pool and Hydroponic purposes etc.

Bought one of these.  We wait and see













CHLORINE
http://arduino.cc/forum/index.php/topic,52017.0.html
Then, how to measure? Absorbance of 530nm light is how it is done in some commercial meters. This is a green, and there are LEDs at this wavelength. You could ....
Syndetic has a very good optical absorbtion sensor.  We could install a suitable wavelength LED.