The test(s) stink. IMO they do not work well, or give numbers over too wide a range to have much meaning. To get an accurate reading you likely have to send your samples to a lab that can do ICP analysis (big $).
There has been a lot of debate about Sr over the years in the hobby. If you have a calcium reactor chances are you are getting some into your tank as the substrate dissolves. Some people have found that if they dump a bit extra in they get a boost in coralline algae growth and sometimes in coral growth, but there have been no controlled experiments run. When Rob Toonen was in town we discussed this and he thought that one of his colleagues had run some experiments, but when I pressed him on it it looks like controlled experiments may have never been run.
There is no question that Sr is incorporated into coral skeletons. The question remains however as to whether there is any Need for Sr. Sr is chemically quite similar to Calcium, so it might be that it just ends up in the coral by 'accident'. FWIW, Sr concentrations and ratio of Sr to calcium and magnesium have varied considerably in the ocean over millions of years.
I've dumped it in myself a few times, but never seen any dramatic benefit (not saying there wouldn't be a benefit to regular controlled dosing mind you). There is no question however that if you dump in enough you can kill critters in your tank, there is a toxic level.