i use an aqualifter pump on a timer to add salt water to my sump daily, i have a 90gal tank and a 80 gal sump with @ 50gal in it. the pump pumps @ 1gal per hour so i run it 2hrs a day, this raises my sump @ 1in. causing my bubble magus to overflow which i have connected to the house drain, the skimmer overflows till the level drops back to normal, i have no ATO, i mix my water to 1.020 and this maintains my tank at 1.025. i perform a monthly vacuuming of @ 10gal as well. the skimmate is light tea coloured when overflowing.
I think it would be best if you added newly mixed saltwater to the sump close to the return pump and after the skimmer as my skimmer tends to go a little crazy when I add the newly mixed water.