Submerged? Cool, glad it didn't fry on you... I would only suggest to take a tooth brush once in a blue moon and lightly clean the sensor... Once the Tunze didn't kick in, and water ran low, but keeping the sensor clean fixed that. And using a toothbrush means you don't have to remove it to clean it.

It wasn't plugged in. I also soaked it in ro/di a few times then let it dry. this was before I even had my tank running =)

Sounds like your entire system is in the basement and if you don't mind having a top off container in the vicinity of the tank, my vote would be to elevate the top off container and do a simple gravity feed ATO through a mechanical float valve. About as simple & bullet proof as it gets and no electricity or pumps involved. The ATO container doesn't need to be very close as long as it's elevated above the level of the mechanical float valve in your sump or display. If there is a concern that the mechanical float valve may fail, keep the ATO vessel to a reasonable size so that the damage will be minimal. I've been using a mechanical float valve for more than two years (Wait brand humidifier valve) and there hasn't been a glitch.