DIY auto water top off?

[CardBoardBoxPro]

I was just wondering is a gravity power auto top off is possible. I am thinking this.

There is a two leader bottle. An air line (with back stop valve) tube goes down to the sump and sits there just above the water line. Another tube goes up to the tank and sits just below the surface of the water. When the water evaporates the water level in the tank drops. This lets air in and the vacuum or the 2 liter bottle is ended and it lets water out into the tank till the water level is back up.

when power is out the sump would jsut have to acomidate the extra 2 liters.

would this work?

[Big Blue Hippo Tang]

Hello, I have a 7gal. water jug above my sump with 1/4 tubing, and in my sump I mounted a CORALIFE float, hook up the tubing, and about once a week fill up the water jug ***or as needed depends on evap.*** B.B.H.TANG