I tried using kalk in my top off water and out didn't work for me. I didn't have to dose as much alk but still had to dose a good bit daily and kalk was messy and a pain in the butt to mess with. Also really had to watch the ph so if you do decide to mess with kalk, you might consider doing it in conjunction with vinegar. But all in all, I would just start dosing alk in your ato. Much easier and more accurate!