I just wanted to clarify something. A drop in calcium is not tied to evaporation. A drop in calcium shows your system (corals, inverts, coraline algae...) is using calcium. If you add more items that need calcium, your dosing will need to increase to keep up. Your evaporation is tied to things like humidity, air movement across the water, air temp. Your evaporation rate will vary some as these things change. Actually if your system wasn't drawing any calcium, the level of calcium would go higher as the water evaporated.