Hi
My system does exactly what you described but also sends the water from the reservoir either through the Kalk reactor or straight to the tank based on the tanks pH.
Here are some pics....if interested let me know and I can explain the system more.
Here is the whole system:
This is the controller that controls the water level in the reservoir...it lets the tank drain until bottom sensor is tripped then fills until top sensor is tripped. There is also an overflow above the top sensor in case it were to stick on.
This is the right side of the water control panel or incoming water control from the RO/DI. Water come in from the back into the 3 way manifold. Orange line feeds Salt water mixing tank, White line feeds a general purpose valve for getting water for cleaning and rinsing things. Blue Line feeds to a solenoid that is controlled by the controller pictured above to fill the reservoir.
This is the left side of the water control panel, it controls where the water from the reservoir is routed. Top solenoid is opened and closed by the float switch in the sump (there is a high and low switch for protection) when the sump is low on water the float switch open the top solenoid to let water flow from the reservoir. Next the water flows through one of the 2 far left solenoids. The first one directs the water through the Kalk reactor and the second one sends the water directly to the sump. Which solenoid is open and where the water is routed is determined by the AC3 based on the pH of the tank, for example if the pH is greater than 8.21 then water is send directly to the sump. If the pH is 8.21 or less the water is directed through the Kalk reactor then to the sump.
Hope that wasn't to ugly of a description....hope it spawns some ideas for you....
einsteins