Now hear me out….I know this sounds like a dumb question but I can’t figure out if “return” means returning to aquarium or returning to sump….I know. I’m an idiot but I need to place this ATO & I’ve been googling for a while to avoid this embarrassment. This is my last resort. Ive had it in the last chamber that returns water to the tank but for some reason last night that water fluctuated. A LOT. Bc the fresh water brought my level up, I took some out but the water in my tank staye high an the water in my sump staye low. Now be put the sensor in the first chamber, where the water enters the sump, but I’m afraid to turn my ATO on now. Please help