So I was doing my weekly tank chores and in the process I needed to make a new batch of kalkwasser top off. I was quite amazed how little Kalkwasser I have used. This container is over 5 years old! I have only used maybe 1/3 of it and I use it all the time in my top off water. I go through 5G of top off water every 4 days and always use kalkwasser. I stopped for a few months just to see if using 2 part was cheaper/better than using Kalkwasser for maintaining Alk/Ca.. bottom line, not even close. Nothing too exciting.. I just wanted to share how long a bottle of kalkwasser has lasted me (looks like it will last me 15 years at the rate I use it, which is 30grams per 5G of water and 80ml of vinegar.)