Kalkwasser solution is highly alkaline with a pH in a fresh saturated solution of 12.4.

This solution must be dripped very slowly into your aquarium or you will experience massive pH swings which will stress the corals and fishes in your system.

Many people who do not have a computer or monitoring system and only check their pH using test kits will be completely unaware of this fact as they perhaps only test once per day.

To keep down cost many hobbyists dispense with a proper dosing unit and simply make up their solution in a plastic bag and hang it over the aquarium at night with a pin hole in it to allow the liquid to come out. This is highly uncontrollable and dangerous for the above reasons.

Another downside of too fast an addition is that you can get local concentrations of calcium which instead of dispersing will drop the calcium out of solution as insoluble calcium carbonate which adds nothing to your system.

If your top up system sticks on then not only will you flood your system with fresh water but more dangerously this water will be at a pH of 12.4 and will wipe out your system.

See the article on use of a timer to prevent this happening.