I've used ATO autotop off as well. it works well, you should set it up so it has a 2nd 'safety' float so if the 1st sticks, the 2nd will turn it off and prevent an overflow. It has diagrams on their website for more info, it's not difficult to do. There are many ways for top off, I'd consider ATO a middle-of-road method, you can do cheaper like tumbleweed mentioned or more expensive, depending on your preferences. I use Litermeter III, it's expensive but I also use it to dose 2-part, so it's like killing 2 birds w/ 1 stone.