I was thinking of doing a kind of reverse overflow, that would siphon water into the tank when the tank level drops, however I am still figuring out the logistics of this. My idea as of right know is putting a small container of fresh water at the same water level as the tank, and attaching it to the tank with a inverted U tube. That way once the water in the tank starts to drop, the water will balance itself out by drawing on water from the freshwater container. I am not sure this will work as I know the water will mix, but I don't know if I will get enough freshwater to compensate for the loss due to evaporation. Right now I am looking for the sensor you mention partypalooza, so thanks for the tip, but I am off work now with a few cracked ribs, so I would prefer DIY as it gives me something to do. Anyways thanks for the advice!