Sr2+ is similar enough in properties to calcium that it can replace calcium structurally (if not entirely functionally) in those enzyme systems that utilize calcium as a substrate. Radioactive strontium was at one time considered as a potential fuel for some nuclear reactors until it was determined that the human body readily makes bone out of it, and thus plant workers who were exposed to even small amounts would have a greatly increased mortality. As far as I know, humans do not require Sr to make bone, and thus deposition is by biochemical accident/mass action.
In all likelihood coral enzymes have as much trouble distinguishing between Sr2+ and Ca2+ and thus there is deposition of both based upon local concentrations of each (mass action). So in other words, if you dose Sr, your corals will have Sr in their skeletons. If you don't, they won't. Whether SrCO3 adds structural stability (and therefore increases growth rate) of coral skeletons is a question for the structural geochemists/inorganic crystallographers to answer (and the answer is probably no).
Personally, I don't think it's worth the effort. I haven't seen significant changes whether I dose Sr or not.
Strontium (Sr++) has been found to be enriched at the growing surfaces of CaCO3 skeletons in certain organsims (Sr++ is close in structure to Ca++). It has been hypothesized, but not proven, that it helps and/or is necessary in the biological calcification process. These studies were published a few years ago.
That said, the hoopla about Sr++ depletion in tanks seems to have dissipated. There are lots of people who have dosed no Sr++ (except via water changes) for years, and their animals and rates of calcification are not appreciably different from people who do dose Sr++.
I also don't think that it has been established that Sr++ really gets depleted in most tanks. If it's necessary, perhaps plenty gets in via Ca++ supplements as an impurity.
Additionally, there are those who believe that Sr++ becomes toxic at levels not much above NSW levels.
Since testing for Sr++ is difficult, my sugestion is to not add any unless you somehow have information that your tank is deficient in Sr++.
[This message has been edited by Randy Holmes-Farley (edited 15 February 2000).]