2-4mm, it starts out as more and after a month or two of use the switch softens and switches at a smaller gap. The main thing to keep in mind is the safety is a time limit so it absolutely should not be used on anything over 55 gallons and is delivered press for a tank under 25 gallons.
I don’t understand why there’s a tank volume limit? I think it will depend on how big the water surface is as the surface area decided the amount of evaporated water between each dosing. I’m just wondering. Thank you!
Because the safety is a timer. If the pump runs more than 1 min 45 seconds or 2 min 45 seconds continuous depending on what you set, it times out, shuts down and will never run again until you power cycle it, this is roughly equal to a 1/3rd or 2/3rd gallon top off. The Nano Osmolator is for small tanks, regular Osmolator is for bigger tanks, with more invested it makes sense to spend what basically is the cost one nice coral more for a safer top off system on a bigger tank. The full size has an additional safety sensor and is more precise and has a longer time limit.