First, I don't need to keep my sump at a constant level as it can function with a variation of up to 20 gallons or so. I keep an eye on the salinity, and adjust the top-off rate of the kangaroo up if the salinity is tending up, and adjust it down if it the salinity is tending down. Once you figure out your average rate, it is pretty easy to keep the salinity very close without using any kind of float switch, with just semi-weekly rate adjustments. I like that as I've read too many posts about stuck floats and excessive top-off water killing the tank. Since the skimmer pulls salt water, it is important to also add salt water on occasion to keep the sump level in the right ballpark. I have the kangaroo pump out of a 15g container filled with kalkwasser, which lasts me 10-15 days depending on the weather (more in winter, less in summer). The kangaroo reads the rate in mL/hour, and can go from around 5 to 300 (4 oz/day to 1.9g/day). To start with just set it for how much you are currently adding per day, and then adjust from there based on observed salinity changes.