Soon I'm going to be away from home for an extended period due to military deployment. I'm not sure how long, but at least six months and maybe closer to a year. My wife will feed the fish for me during that time, but with two small kids I'm not sure I can count on regular water changes. I'd like to leave at a minimum an automatic top-off system to prevent the pump from cavitating. There should be enough plants to take up nitrate for this period, and the tank is lightly stocked enough to make this reasonable.
The tank is a 75 gallon with 55 gallon sump, unheated.
What I want to do is set up a trash can full of dechlorinated water, with a pump in it, that will turn on when the water level in the sump reaches a certain point, and then turn off before it overflows. All the commercially available float switches I can find are designed for sump pumps to start the pump on a high water level and turn it off at the low level. It seems like it might work to just install the thing upside down, but I haven't been able to look at one out of the box to be sure it would work as I expect. Does anyone have any experience with these, or maybe could suggest a product I've missed? Here's one I'm looking at: http://www.acehardware.com/product/index.jsp?productId=3706348