You have a couple options,
Reefsupplies.ca is a good source for bulk media, calcium and sodium carbonate, it's the canadian BRS.
Or you can go the route of de-icings salts as per Randy Holmes
http://reefkeeping.com/issues/2006-02/rhf/index.php
I've gone both directions here but I've gone on the second option for the past 4 years mainly because I was able to get a 20kg bag of sodium carbonate which is more difficult to get (or make) than calcium chloride and magnesium chloride. Ease of acquiring the media dictates the direction I would go.
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