Has anyone made a DIY PH Regulator.

Where can you get cheap PH sensors?

Hook up the PH sensor to a micro controller and connect that to control the CO2 solenoid.

You might be able to make a PH controller for the cost of the sensor plus $20 to $50. Maybe even cheaper if you use a PIC micro controller.

Check this out:

https://www.plantedtank.net/forums/sh...ght=CONTROLLER

This may be TOO cheap, but:

http://www.thekrib.com/Plants/Fertilizer/