WOW... Thanks for the information, looks far more complex than mine (or at least I'm still stumped however).

My ATO (RO/DI) tank is a separate 150 gal tank which does not have any sensors and only has a line going to a dosing pump (Pump 1) which fills my sump if Level 1 shows low (currently set to ATO Only)
My Salt water tank is a 50 gal drum (manually filled with RO/DI and mixed with salt) - this tank also has no sensors and only has a line to a different dosing pump (Pump 2) and into my sump
Then I have a 3rd dosing pump (Pump 3) which is in my sump and will pull water from sump into house drain

Currently Level 1 (located in my sump) is set to ATO Only, I think I need to change this to ATO and Water Change. Currently when the water level drops below Level 1 Sensor, Pump 1 turns on and tops off (with RO) my sump.

I have a second sensor Level 2 (also located in my sump and set about 2 gallons below Level 1)

My plan is to have it such that once a day (during night) a 2 gallon water change happens. Pump 3 turns on and pulls 2 gallons (down to Level 2 sensor, but no longer than 2 hrs) of old water from sump to the house drain. Once Level-2 sensors sees that the water level in sump is at below its level it would shut off Pump 3 and activate Pump 2 (pump that pulls in new salt water). Pump 2 would fill sump with new salt water until Level-1 sees water at its level (but no longer than 2 hrs) = water change complete.

For some reason, my brain is not grasping just how to set this up in the Profilux... Sorry

Also - Im assuming that by setting Level 1 to ATO and Water Change - they system will NOT try to fill (ATO) while the water change is taking place