I dose the SeaChem Advantage Calcium. Every tank will have different needs depending on your corals, etc. I first dosed it manually for a couple months, adjusting the amount with each test until it stayed steady. Then I mixed it in a 4L jug, which I set to dose over a 1 month period. I currently use 400 ml of the powder mixed in the jug and it takes about one month before I need to refill the jug again. My Ca is pretty rock steady ( near 400 ppm). It varies a little after a water change, but not much. This is for a 100g tank.
The SeaChem site page for that product has very good instructions on how to use it.
http://www.seachem.com/Products/prod...dvCalcium.html