Easy and Effective Automated pH Controller

  • Using the Milwaukee Model SMS122 pH Controller to make an automated pH controller. It is quick an relatively inexpensive (around $125 to $150) to put together an easy system like the one shown above.
  • The system is designed to lower pH only. Most of the time a lower pH is what is required for hydroponic systems. The above system could be modified with the use of a relay so that it could adjust the pH up (more alkaline).
  • The system is simple. The pH controller monitors the pH of the system. When the pH raised above the set point than you have selected the Controller turns on a small pump that is placed inside a bucket with a diluted acid mixture (water and Phosphoric Acid usually). The pump delivers acid solution to the reservoir until the pH drops to your selected set point. The controller then shuts off the pump.
  • You should have very good circulation in the reservoir so the acid will mix quickly with the nutrient solution. This is important so that the controller gets an accurate measurement of the pH.
  • You should use a diluted acid solution. The reason for this is simple. It takes relatively small amounts of pH adjuster to make big swings in pH. If you use too strong of an acid solution the controller may not shut off the pump in time and the pH will drop well past the pre-set limit. For this reason I would recommend putting a valve inline so the flow can be reduced to drips. I usually take the stock liquid pH adjuster available from most Hydro shops and dilute it to 1 part pH adjuster to 8 parts water. Each situation is different so some trial and error may be required to get the system “tweaked” to your personal needs.
  • I like to make a Styrofoam float for the probe to keep it from sitting on the bottom. It makes for a more accurate reading.
  • You can always add another pH controller to the system for a back-up in case the primary controller malfunctions. You select a slightly lower set point for the back-up controller. You plug the primary controller (with the slightly HIGHER setpoint) into the controlled outlet of the back-up controller. Than if the primary controller malfunctions and stays on the secondary (back-up) controller will shut the acid pump off.