This is simple programming in an apex, with a BOB, and a float switch.
Lets assume your float is on switch 1, and your return pump is on an eb8. In your return outlet programming you would simply place this line.
If SW1 open then off
Open or closed depending on how your switch is wired and if its a normally open or normally closed switch.
+1 on Apex with floats.
Below uses 3 floats in the Return section of the sump
So this is the code on Return pump Outlet (shuts off Return Pump if the Return Section water level gets low)
Fallback ON
(Outlet ReturnLow_A3 is virtual outlet connected to float valve)
If Outlet ReturnLow_A3 = OFF Then ON
If Outlet ReturnLow_A3 = ON Then OFF
And here is the code on the Skimmer Outlet (shuts off skimmer when the Return Section water level is high - prevents skimmer overflow if the Return pump stops)
Fallback ON
(Outlet ReturnHi_A2 is virtual outlet connected to float valve)
If Outlet ReturnHi_A2 = ON Then OFF
If Outlet ReturnHi_A2 = OFF Then ON
And here is the ATO Outlet
Fallback OFF
(Outlet ATO_5 is a virtual outlet connected to float valve)
If Outlet ATO_A5 = ON Then ON
If Outlet ATO_A5 = OFF Then OFF
If Outlet ReturnHi_A2 = ON Then OFF
If Outlet ATOResLo_A4 = ON Then OFF
Defer 002:00 Then OFF
If FeedD 120 Then OFF (I use the Feed button "D" to disable ATO after filling and mixing in Kalk - lets the calk settle)