I read that earlier (and a few times before haha). I am sorta on the thought that its either like you said that corals use it "by accident" instead of calcium, or that it is a means to get rid of it (by placing it, similar how it is thought that early life may have made first exo skeletons with phosphate but went extinct as it wasn't as available as something like calcium carbonate), or that it acts as a way for corals to have more elements that they can use for their skeleton as to not limit them to just calcium.
Regardless, I figured its something that is probably not harmful by any means to have at least some. I have been reading a lot lately to try and figure out everything that I would like to dose in my tank. I am currently satisfied with using seachem reef builder for alk and chaetogro for trace elements (and magnesium as this seems to keep that up) (it also seems to contain what I read in a couple of macro algae phytochemical analysis papers). I also dose red sea iodine (trace color A), with iodine, bromine, and fluorine, though usually less than 0.5ml a day (I dose this as from what I understand it is a common element in macro algaes). However I was debating whether to continue with red sea calcium plus or to try and use calcium chloride with strontium mixed in the solution. My only concern is that I would have no clue how much of the strontium to mix into a 1 gallon container of BRS calcium chloride. The reason for switching is simply that its cheaper.
