Here is a question, for the past 2 weeks my calcium has been at 440. Today when I tested it, it was at 540! (what a great coincidence this thread is) I did a water change on the tank, but I have NO idea how my levels got so high!! They have never been that high. Generally if anything, they are a bit low because of that damn calcium loving algae I have in there. Any ideas how this happened? My test kit isnt old, honestly its less than 6 months old. The only thing I have changed is I went from using Instant Ocean to Oceanic salt mix. But I havent done a WC in 3 weeks.