This is another Instructable, this time from user matthewh415.

(It) uses the IBC method of Aquaponics, with modifications to include a Raspberry Pi for controlling a pump, solenoid drain, and temperature probes for water and air temperatures. The relays and timing is controlled with Python scripting. Temperature and control data is collected every minute and sent to plot.ly for graphing, and future expansion will include sensors for water level and PH values for additional control.

Read the full Instructable here