If the evaporated water loss is from the aquarium is replaced with kalkwasser then it will add calcium and offer the other benefits described above. The solution however is highly reactive with CO2 in the air forming insoluble calcium carbonate. The reaction with CO2 significantly reduces the free calcium ions from 900mg/l in the fresh solution at pH 12.4 to 5-6mg/l at pH 10.
For this reason it is necessary to continually make a fresh solution and to keep it away from the atmosphere. This is where a Deltec Kalkwasser stirrer may come in to play as it makes up fresh saturated solution as it is used up. It is alsoCommonly use in junction with a Calcium reactor to help stablise the water chemistry in a reef tank.
Note that great care must be taken when administering Kalk due to the great affect that it has on the pH of the aquarium.
Kalkwasser is ideally dosed after the lights have gone out on the aquarium to counter the natural drop in pH which occurs when photosynthesis stops.