Quote Originally Posted by longhorn_20m View Post
What is the benefit of draining during refill?
The Kalk reactor stays full with water all the time. By having the drain, it allows you to remove water more easily (less mess and hair pulling) to make room for more Calcium Hydroxide.

The water can only hold so much Calcium Hydroxide in solution so you can add extra to the reactor. When the stirring pump kicks in, it remixes it to maximize how much is kept in solution.