For mixing Kalk for top off I just dump some lime in the 5 gallon RO jug, add some vinegar, let it settle, and start the drip.
I have run a whole 5 gallon jug into my 55 gallon in less than 1 hours before. I had to do several large water changes and add vinegar to get the pH back. Be very careful when you are changing pH as any wrong move can cause Calcium precipitation and that will crash your water chemistry.