Well you say the thing turns on every minute. And if you turn it on every 10 minutes, you're still turning the thing on/off 144 times a day.
Do this as a check, grab the hose that drips water into your tank, and simply measure how much goes in everytime it pops on, you probably aren't evaporating that much. The thing with single trigger ATO systems is you top off until the float pops up, but at most get a couple drops more than it needs, so yeah when 3 drops of water evaporate, you end up having to fire it up again... pumping it up 3 feet of head, before putting those 3 drops back into the tank.
If you need more water do OSC 2/30 then