Kalk does not cause problem, however they are sensitive to pH change.
In the past at one time, I used Kalk reactor but not with a continues feed pump. Rather I have a pump which pump at a fix rate. I have a timer that pump the kalk in. I adjust the amount by increase or decrease the duration it pump, 4 times a day.
Anyway, the timer mal function and stuck on ON for about 4 hrs by the time I detected it result in a mild to moderate Kalk overdose. I did not check pH of the tank (this is one value that I don't follow). I only have SPS, LPS, Xenia and Magnifica, and clams in tank at the time. The species that cause me to look around and see what was wrong is the Magnifica. He just does not look right. Everything else looks fine. Everybody recover well without further problem after I fix this issue.
I learn not to depend too much on timer after this, especially the China made mechanical ones from Home Depo. It can kill your tank. Another time, the timer control the MH light stick on over the weekend at my office tank and bleach all my corals and sicken my fishes. It was much harder for me to find this problem out since it was my office tank which I don't see at night. Same problem, bad timer. I do away with all of these other than occasional use in treatment tank these days.