About 1 gallon a day. I know my kalk amount is low but that is what my tank needs to stay stable and it works very well. DD H2Ocean as I have tested it Ca 460, Alk 10, Ph 8.3, Mag 1380. I have coraline exploding again in my overflow and back glass and my sump was growing it quite fast while I had the fuge light on. I mag float my glass every day so nothing can really start to grow, not that it needs it not much algae on the glass ever. I will be closely watching my mag to see what is going on. I agree it does seem off to be using that much. My test kit is new by the way, got it a few weeks ago.