Just another point. Here are the alternatives:

1. Magnesium Chloride - good product, but it will only add to the chloride buildup issue. Chlorides don't cycle like sulfate.

2. Magnesium Sulfate - See above.

3. Starve your corals for mag. Another issue is that magnesium plays an important role in helping to maintain the calcium/alkalinity balance in the aquarium. Not enough mag and you end up with a calcium carbonate precipitation problem. That means crashing levels of both calcium and alkalinity, burned up pumps, and a nice white tank that will look more like Fargo, ND in January then a reef in Tahiti.