A DIY EC probe is pretty much essential considering the extremely high cost of buying one. After a bit of experimentation i've found a solution that works extremely well, gives accurate readings and costs less than $15. The video below explains exactly how to build your own.
At long last the Arduarium Controller is starting to take shape. As previously stated there is going to be two different versions (Basic and Ultimate). The only difference between the two is that the ultimate will include an EC circuit so you can measure salinity.
Below are the pictures of the PCB's. The basic version is 95% completed and will be going to fab shortly. All of the circuits on it have been thoroughly tested (which is why the Ultimate version won't be coming out until several weeks after the Basic version).
The Arduarium Controller Basic has been designed to take care of everything that you may be interested in with an aquarium, aquaponics setup, hydroponics setup etc. Expandability, function and cost have been the three largest factors that were considered when designing this board.