Yes, then an autotopoff.com unit is what you want. I actually run one of these since I have 2 pumps for topping off (one for kalk and one for fresh RO/DI). The way my setup is the pump for kalk is set up as a multi timer and is plugged into the ATO.com unit with an alarm set for pH to turn off if it's above 8.35. The pump for RO/DI is set up as a multi timer and plugged straight into the PC-4 with an alarm set for the float switch. The key is the RO/DI pump is timed to come on after the kalk pump turns off.
The overall effect is when my ATO kicks in, it tops off with kalk. Either the float switch on the ATO.com unit will stop the pump, or the pH alarm will stop the pump, or it will time out (never had that happen). Then the pump for RO/DI activates. If the water level was achieved with the kalk top off, nothing happens. If the pH spiked and the kalk pump was turned off, then the tank will still top off with RO/DI, meaning I don't have my pump run dry or make bubbles.