Added another five gallons today (really four gallons cause I don't fill the bucket to the top).
There must be a way to test the concentration of the coolant. I'm blindly adding water / Rustlick at a ratio of two cups per four gallons each time. If only the water is evaporating then the mix is getting more concentrated over time. There must be a way to test the concentration so that it can be kept at the right ratio.
Well, worst case, a more concentrated mix is better - I think.