If you use it, start very slowly. Ammonia is a substantial concern in magnesium chloride. You could also try measuring it directly, as I did here for Dowflake:
Purity of Calcium Chloride
http://www.advancedaquarist.com/issues/mar2004/chem.htm
from it:
Ammonia Testing
There are several ways that calcium chloride can be prepared on an industrial scale. One of these (the Solvay process) involves ammonia. Consequently, ammonia has the potential to be present as an impurity in calcium chloride. For that reason, I tested each of the calcium chloride samples for ammonia. I used two different kits to test for ammonia: LaMotte and Red Sea. The results of the Red Sea kit are shown in Table 4.
Samples spiked with ammonia (from a standard containing 5.8 ppm ammonia as ammonium hydroxide in water) did not show as much ammonia as the test kit claimed, but it was clearly detectable in the two spiked samples (Dow and Kent Turbo Calcium). These spiked samples contained an extra 1.9 ppm of ammonia. One showed up as 0.5 ppm ammonia, and the other showed as 0.5-1 ppm. Since all of the unspiked samples showed 0.5 ppm or less of ammonia by the kit, I conclude that these samples have less than 3 ppm of ammonia in them as tested (accounting for dilution).
In short, none of these samples showed enough ammonia to be concerned about, even when adding enough to boost calcium by 200 ppm in one day. Since these solutions were 100,000 ppm in calcium, adding 200 ppm calcium to an aquarium entails adding 1/500th of the tank volume. At 3 ppm ammonia in the supplement, that means that the tank will be boosted by 3/500 = 0.006 ppm of ammonia, which I believe to be largely insignificant in a reef aquarium.