depends on your tank. whats your coral load like? any clams?
i dose kalkwasser basically everynight. i add calcium via purple up about 2-3 days a week. 1 cap full in my 40 gallon system. im also runnig all sps corals, so i have a high demand for calcium.
thing wiht kalkwasser, is it doesnt raise calcium. you have to add calcium, get it where you want it, then add kalkwasser to keep the calcium at that number. by doing this, your magnesium levels are diminishing, so you will most likely need a magnesium additive as well. i use seachem magnesium. its sort of grainy. i just mix it with some ro/di water and dose that into my sump. id like to pick up a liquid magnesium additive because it would be easier to dose that than dissolve the granules ive been using.