Is topping off coolant even a real thing you need to do? Most modern cars have a sealed system, so if you're losing fluid that often, you've got a leak or a head gasket problem, not a topping off problem. Thirty minutes of fiddling with that plastic reservoir just sounds like you were bored. I've never topped mine off once in 100,000 miles, and the temp gauge stays right in the middle. Maybe you were just creating a problem that didn't exist so you'd have something to fix.