I have been building a hydroponics controller around Arduino Mega for a while now, It has a HTML5 user interface done with backbone.js and jQueryMobile for setting up the machine and log viewing. The whole thing works as standalone without a additional computer or server.
I have been doing test runs for the past week and I think I'm ready to put the plants in and start growing.
Many things still need improvements and refactoring.
Algorithm at work: First the amount of nutrients have been adjusted to be followed with pH. You can see how it waits for the solution to get stabile before adjusting again.
More info can be found here:http://www.cs.helsinki.fi/u/ljlukkar/hydrobot/