purple up?

[DanG]

Your best bet is to get a good calcium test kit (I really love the salifert Ca test kits).
Take a measurement, add one cap of purple up, wait about half an hour to make sure it's been spread around, then take another measurement. That will give you an idea how much one cap will raise your calcium. You don't want to raise it any more than 25ppm per day.
It's also a good idea to take a measurement about 24 hours after you dosed with it, just so you can get an idea how much calcium your system uses in a day.