Jamey, a solenoid is not typically used as a safety device in case of power failure. It's rather expensive to be used for that purpose alone. Besides, the flow from the reactor would be stopped and the CO2 would mostly stay in the reactor chamber.
Like you stated, the solenoid operates a gate valve. When power is supplied, the gate opens and CO2 exits the regulator. When power is swithed off, the gate closes and no CO2 will exit the regultaor.
A solenoid is designed to be used with a pH controller or a timer. Many users can not afford or understand the concept of a controller and simply use a timer to run the reactor about 16 hours a day.
The most accurate use of a Ca reactor system is to use a pH controller to mangae the system. The outflow of kalk water is acidic and this is dripped into an effulent jar with a pH probe. As the Kalk concentration increases, the pH will decrease. The controller is set at a specific control point, like 6.4pH. When the pH drops below this range, the controller shuts power off to the solenoid and CO2 gas is switched off. Slowly the concentrion of kalk water exiting the Ca reactor will begin to rise. Once ot goes above another set point, say 6.8, the controller will send another signal to switch the solenoid valve back on, thus CO2 will enter the Ca reator and the chemical process of converting CaCO3(s) to Ca+ (aq) begins all over again.
It should be noted that many people run reactors 24/7 without problems. In a sence, they are blindly adding Ca+(aq) to their system. If too much is added at one time, the Ca ion can expend the buffers in the water and thus reduce the ability of your system to counterbalance small fluctuations in pH, which is detrimental to the animals. This is known as a system crash. A pH controller just gives the user more control, and can eliminate crashes due to a lack of awareness in the total amount of Ca+(aq) added to the system.
When using a reactor, tank Ca levels, pH, and dKH should be monitored frequently. Akalinity (dKH), is the buffer capacity-the more buffer you have, the more your tank water will be able to resist sudden pH fluctuations)
Hope this helps.
Cheers,
Scott
