I don't add anything but water to make up for evaporation, and I do water changes. I think Kalk is for reef calcium, if I remember correctly. I don't think fish need it.
After reviewing posts here and in the fish disease forum, I am considering adding garlic, beta glucen and/or selcon by soaking food before feeding, as all these help fish have better immune systems generally.
I think the water changes replace minerals, etc. that fish may need.