[Canadian]

You can dump it straight in to a sump if you ensure you're not dosing large amounts that will drive pH up by more than 0.2. Dosing a kalk slurry was popularized by Anthony Calfo and it has some reported benefits. I've never employed this method but there are a lot of hobbyists who have without killing their livestock.

From wetwebmedia.com:

Kalk dosing
Hello and thanks for all of your helpful hints and suggestions!! I am now bringing my pH up to acceptable levels with the Kalk dosing. Was 7.9 and now am keeping it up to 8.25 regularly.
<good to hear... do check recent posts on the FAQs also about low pH and well insulated houses (atmospheric influence) and opening a window to raise pH in the aquarium!>
The question I have with the Kalk "slurry" is: Do you mix up the solution and then dump all contents from the glass into the aquarium or do you pour it slowly and stop when the undissolved Kalk starts dripping in? This has been a bit vague in your Q&A forum.
<no worries... both ways can be done. I elaborate on this application in my Book of Coral Propagation if you are inclined. The gist of it though is that it is not so much a matter of slurry or decanted solution, but rather what is your daily demand for calcium (go three days without any dosing and measure calcium before and after then divide by three to get a daily average). Once we figure out how much calcium is needed daily, we then need to slowly dose calcium to fulfill that demand (confirmed by testing that reveals the calcium level isn't straying downward with your x mg of Kalk daily). You could begin with an eight or a quarter of a teaspoon daily (probably a little low if you have a good bit of live rock and/or coral). The only limiting factor here is that regardless of what your daily demand for calcium is, you should never add more slurry or decant than your pH can sustain without jumping my more than .1-.2 (i.e.- before slurry 8.2, after slurry 8.35). For such measures and experiments with Kalk slurries, accurate pH testing equipment is necessary (digital pen or meter). It is uncommon that your tank will not be able to get all of its daily calcium needed through a single dose without spiking pH. Only tanks with massive coral loads need a second dose or more. Remember to only dose Kalk after the lights are out tooThanks as always, Jeff Reed>
<best regards, Anthony>

And here's a link to lots of answers to kalk questions by Anthony Calfo. Many of them pertain to dumping in a slurry:

http://www.wetwebmedia.com/kalkh2ofaqs.htm