I wanted to share this, as it addresses a couple of common issues people have in their reefs, especially SPS-dominated reefs....
A couple of months ago, I switched from dosing Seachem Reef Complete (SRC), which I had been using for several years, to BRS Calcium Chloride to save some money (actually, a lot of money). I never dosed Magnesium specifically because I always thought the SRC would take care of that (SRC also includes Magnesium & Strontium), but with the switch to BRS Calcium Chloride, I needed to also start dosing Magnesium.
So here I am a couple of months into dosing Magnesium and I have to say, it's important. I previously used to describe my corals as "great color, decent polyp extension, slow growth". Color continues to be great, growth rates have visibly increased, but the biggest difference by far is the polyp extenstion. My Milli's, Prostrata, and Red Planet are quite "shaggy" now with pronounced polyp extension. I have a Neon Green Montipora Spongodes colony that looks almost brown, but not because of color loss; the brown polyps are so big/extended that they cover most of the colony now.
I recently researched Magnesium and I read several forum threads where Magnesium was suggested to people complaining about poor polyp extension. It bascially confirmed what I was already seeing, so as it turns-out, I just happened to accidentally stumble upon the benefits of this very important additive because I was trying to save a couple of bucks.
Also, I asked around Reef Central (Randy Holmes-Farley & others) and found-out you can mix Calcium Chloride and Magnesium Chloride (important: both have to be "chlorides"), which is great because I can still use only one dosing pump for these additives. In a 1g container, I mix 2.5 cups of BRS Calcium Chloride and 1.5 cups of BRS Magnesium Chloride, but you can experiment with your own recipe.