Kalkwasser is calcium hydroxide. It's used to help maintain ca and alk levels. You mix the powder with r/o water and wait for it to settle. It ends up leaving you with a liquid calcium hydroxide that you drip at a slow rate. 1 drip per every second or two is fine. You still will need to raise ca and alk levels on occasion when you drip kalk, but overall it does a good job of keeping your levels stable.