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.
I love how projects evolve. Several people stumbled upon my Arduarium Controller (which I designed geared towards reef aquariums) suggested that the board would also work as an excellent aquaponics controller. I became interested in aquaponics after learning about it and will be setting up my own small (20gal) which I will document here. Several people will also be documenting there larger systems setup which I'll post here as well.
Finding a waterproof DS18B20 temperature sensor can be a real pain... and it's quite fun to build your own! It only takes a couple minutes of your time and the finished product works great (I've had my original running for close to 2 years).
Page for the MacroDuino project. The aims of this project are to make it easier to get a project up and running without writing any (hopefully) code. The vision behind it is to be able to put a couple shields on an arduino, upload a sketch and have it doing what you want without spending time writing code and debugging. You could also think of it this way: if the Arduino is a rapid prototyping device than the MacroDuino code is rapid coding. You spend 5 minutes setting up the code and configuring it and you're done.
The Arduarium Controller has been designed to be a modular controller that allows you to pick and choose what types of inputs and outputs you'd like for your aquarium. There has been some great code written for it called MacroDuino which allows you to configure the controller to do what you want without having to write a single line of code. Settings are stored in EEPROM so if the power goes out it continues working as you had it setup before.