I use a float sensor wired into an extension cord. A Tom's aqualifter is plugged into the cord. When juiced, the aqualifter pulls water from a 5 gallon jug. Total cost is about $25.

I have three jugs, one with Ca, the second with RO-DI, and the third with ALK. I switch back and forth between solutions -- 1,2,3,2,1 and so forth.

I use a second sensor higher up as a back up. another $9 or so.

Maintenance is cleaning the switch every so often to make sure those micro snails don't block the movement of the float. A little vinegar is all it takes.

The only other issue is that the outlet has to be higher than the jug of water or it will gravity feed into the sump as the aqualifter doesn't block that.